[FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Leandro Santiago]

This is a POC/prototype that aims to enable out of tree filters on
FFmpeg.

Here I name them "extra filters".

It introduces the program `jq` as a new build dependency.

To test it, create a directory, for instance, /tmp/my-shiny-filter/ and
inside it, create the following files:

`filter.json`, with the content:

```
{
  "check": "require_pkg_config json json-c json-c/json.h json_c_version_num",
  "symbols": ["ff_vf_foo", "ff_vf_bar"]
}
```

`filter.mak`, with the content:

```
OBJS += vf_shiny.o
LIBOBJS += vf_shiny.o

libavfilter/vf_shiny.o:
        $(CC) $(EXTRA_FILTER_FLAGS) -c -o $@ $(EXTRA_FILTER_FOO_LOCATION)/vf_shiny.c
```

`vf_shiny.c` file, with the content:


```
#include "libavutil/internal.h"                                                                                                                       
#include "avfilter.h"                                                                                                                                 #include "filters.h"                                                                                                                                  
#include "video.h" 

const FFFilter ff_vf_bar = {
    .p.name        = "bar",
    .p.description = NULL_IF_CONFIG_SMALL("Example filter Baz"),
    .p.flags       = AVFILTER_FLAG_METADATA_ONLY,
    FILTER_INPUTS(ff_video_default_filterpad),
    FILTER_OUTPUTS(ff_video_default_filterpad),
};

const FFFilter ff_vf_foo = {
    .p.name        = "foo",
    .p.description = NULL_IF_CONFIG_SMALL("Another foo filter"),
    .p.flags       = AVFILTER_FLAG_METADATA_ONLY,
    FILTER_INPUTS(ff_video_default_filterpad),
    FILTER_OUTPUTS(ff_video_default_filterpad),
};
```

Then, from the ffmpeg source tree, run configure specifying where the
extra filter is located:

```
./configure --extra-filter=/tmp/my-shiny-filter
make ffplay
```

Now you can use the filters:

```
./ffplay /path/to/file.webm -vf 'foo,baz'
```

What works:

- Building C based filters with no extra dependencies.
- Multiple filters in the same object file.

What does not work:

- The extra filters will not use the same CC flags used to build the
  built-in filters as I could get it to work yet.
- Due to the above limitation, you cannot include headers of extra
  dependencies, for instance, `json.h` in the example.
- You can pass arbitrary CFLAGS or LDFLAGS in the filter.json file,
  but they should be passed only then building/linking `libavfilter`,
  instead of other libraries.

What was not implemented:

- I believe it would be useful to check if the license of the filter is
  compatible with the license used to build FFmpeg.
- Only extra filters written in C (maybe C++?) are supported for now.
  One of my goals is to enable Rust as well.

Signed-off-by: Leandro Santiago <leandrosansilva@gmail.com>
---
 .gitignore               |  3 ++
 configure                | 61 ++++++++++++++++++++++++++++++++++++++++
 libavfilter/Makefile     |  4 +++
 libavfilter/allfilters.c |  1 +
 4 files changed, 69 insertions(+)

diff --git a/.gitignore b/.gitignore
index 9cfc78b414..4963e90191 100644
--- a/.gitignore
+++ b/.gitignore
@@ -43,3 +43,6 @@
 /tools/python/__pycache__/
 /libavcodec/vulkan/*.c
 /libavfilter/vulkan/*.c
+/ffbuild/extra-filters.txt
+/ffbuild/extra-filters.mak
+/libavfilter/extra_filters_extern.h
diff --git a/configure b/configure
index 750c99e3b9..6a2adc6c05 100755
--- a/configure
+++ b/configure
@@ -179,6 +179,7 @@ Individual component options:
   --enable-filter=NAME     enable filter NAME
   --disable-filter=NAME    disable filter NAME
   --disable-filters        disable all filters
+  --extra-filter=/foo/bar  add extra filter from directory. This option can be used multiple times
 
 External library support:
 
@@ -1798,6 +1799,7 @@ AVDEVICE_COMPONENTS="
 
 AVFILTER_COMPONENTS="
     filters
+    extra_filters
 "
 
 AVFORMAT_COMPONENTS="
@@ -4382,6 +4384,8 @@ do_random(){
     $action $(rand_list "$@" | awk "BEGIN { srand($random_seed) } \$1 == \"prob\" { prob = \$2; next } rand() < prob { print }")
 }
 
+rm -f ffbuild/extra-filters.txt
+
 # deprecated components (disabled by default)
 disable sonic_encoder sonic_ls_encoder
 
@@ -4457,6 +4461,10 @@ for opt do
                 die_unknown $opt
             fi
         ;;
+        --extra-filter=*)
+            filter_path="${opt#--extra-filter=}"
+            echo "$filter_path" >> ffbuild/extra-filters.txt
+        ;;
         --list-*)
             NAME="${opt#--list-}"
             is_in $NAME $COMPONENT_LIST || die_unknown $opt
@@ -4487,6 +4495,36 @@ for opt do
     esac
 done
 
+find_extra_filters_extern() {
+  # TODO: handle invalid filter
+  while read f; do
+    jq -r '.symbols[]' < "$f/filter.json" | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]_]\{1,\}\)/\1_filter/'
+  done < ffbuild/extra-filters.txt
+}
+
+EXTRA_FILTER_LIST=$(find_extra_filters_extern)
+
+for n in extra_filters; do
+    v=$(toupper ${n%s})_LIST
+    eval enable \$$v
+    eval ${n}_if_any="\$$v"
+done
+
+FILTER_LIST="
+    $FILTER_LIST
+    $EXTRA_FILTER_LIST
+"
+
+AVFILTER_COMPONENTS_LIST="
+    $AVFILTER_COMPONENTS_LIST
+    $EXTRA_FILTER_LIST
+"
+
+ALL_COMPONENTS="
+    $ALL_COMPONENTS
+    $EXTRA_FILTER_LIST
+"
+
 for e in $env; do
     eval "export $e"
 done
@@ -7165,6 +7203,10 @@ enabled rkmpp             && { require_pkg_config rkmpp rockchip_mpp  rockchip/r
                              }
 enabled vapoursynth       && require_headers "vapoursynth/VSScript4.h vapoursynth/VapourSynth4.h"
 
+while read f; do
+  # NOTE: this eval is dangerous, as it allows arbitrary code execution!
+  eval $(jq -r '.check // true' < "$f/filter.json")
+done < ffbuild/extra-filters.txt
 
 if enabled gcrypt; then
     GCRYPT_CONFIG="${cross_prefix}libgcrypt-config"
@@ -8243,6 +8285,12 @@ for entry in $LIBRARY_LIST $PROGRAM_LIST $EXTRALIBS_LIST; do
     eval echo "EXTRALIBS-${entry}=\$${entry}_extralibs" >> ffbuild/config.mak
 done
 
+echo "" > ffbuild/extra-filters.mak
+
+while read f; do
+    echo "include $f/filter.mak" >> ffbuild/extra-filters.mak
+done < ffbuild/extra-filters.txt
+
 cat > $TMPH <<EOF
 /* Automatically generated by configure - do not modify! */
 #ifndef FFMPEG_CONFIG_H
@@ -8330,6 +8378,19 @@ cp_if_changed $TMPH libavutil/avconfig.h
 # ...
 eval "$(sed -n "s/^extern const FFFilter ff_\([avfsinkrc]\{2,5\}\)_\(.*\);/full_filter_name_\2=\1_\2/p" $source_path/libavfilter/allfilters.c)"
 
+rm -f libavfilter/extra_filters_extern.h
+
+# Handle extra filters
+while read f; do
+    eval "$(jq -r '.symbols[]' < "$f/filter.json" | sed 's/^ff_\([avfsinkrc]\{2,5\}\)_\([[:alnum:]]\{1,\}\)$/full_filter_name_\2=\1_\2/')"
+    jq -r '.symbols[]' < "$f/filter.json" | while read symbol; do
+      echo "extern const FFFilter $symbol;" >> libavfilter/extra_filters_extern.h
+      echo "EXTRA_FILTER_$(echo $symbol | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]]\{1,\}\)$/\1/' | tr a-z A-Z)_LOCATION = $f" >> ffbuild/extra-filters.mak
+      echo "LDFLAGS += $(jq -r '.ldflags // ""' < "$f/filter.json")" >> ffbuild/extra-filters.mak
+      echo "CFLAGS += $(jq -r '.cflags // ""' < "$f/filter.json")" >> ffbuild/extra-filters.mak
+    done
+done < ffbuild/extra-filters.txt
+
 # generate the lists of enabled components
 print_enabled_components(){
     file=$1
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 7c0d879ec9..9b22aece3a 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -27,6 +27,10 @@ OBJS = allfilters.o                                                     \
 include $(SRC_PATH)/libavfilter/dnn/Makefile
 include $(SRC_PATH)/libavfilter/vulkan/Makefile
 
+# extra filters handling
+include $(SRC_PATH)/ffbuild/extra-filters.mak
+EXTRA_FILTER_FLAGS = -I$(PWD) -I$(PWD)/libavfilter $(CPPFLAGS) $(CC_DEPFLAGS)
+
 OBJS-$(HAVE_LIBC_MSVCRT)                     += file_open.o
 OBJS-$(HAVE_THREADS)                         += pthread.o
 
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 740d9ab265..e8565de5b0 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -621,6 +621,7 @@ extern  const FFFilter ff_vsrc_buffer;
 extern  const FFFilter ff_asink_abuffer;
 extern  const FFFilter ff_vsink_buffer;
 
+#include "libavfilter/extra_filters_extern.h"
 #include "libavfilter/filter_list.c"
 
 
-- 
2.48.1

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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Leandro Santiago]

This is a follow-up to the my previous message:

https://ffmpeg.org/pipermail/ffmpeg-devel/2025-March/340895.html

On 3/13/25 13:18, Leandro Santiago wrote:
> This is a POC/prototype that aims to enable out of tree filters on
> FFmpeg.
>
> Here I name them "extra filters".
>
> It introduces the program `jq` as a new build dependency.
>
> To test it, create a directory, for instance, /tmp/my-shiny-filter/ and
> inside it, create the following files:
>
> `filter.json`, with the content:
>
> ```
> {
>   "check": "require_pkg_config json json-c json-c/json.h json_c_version_num",
>   "symbols": ["ff_vf_foo", "ff_vf_bar"]
> }
> ```
>
> `filter.mak`, with the content:
>
> ```
> OBJS += vf_shiny.o
> LIBOBJS += vf_shiny.o
>
> libavfilter/vf_shiny.o:
>         $(CC) $(EXTRA_FILTER_FLAGS) -c -o $@ $(EXTRA_FILTER_FOO_LOCATION)/vf_shiny.c
> ```
>
> `vf_shiny.c` file, with the content:
>
>
> ```
> #include "libavutil/internal.h"                                                                                                                       
> #include "avfilter.h"                                                                                                                                 #include "filters.h"                                                                                                                                  
> #include "video.h" 
>
> const FFFilter ff_vf_bar = {
>     .p.name        = "bar",
>     .p.description = NULL_IF_CONFIG_SMALL("Example filter Baz"),
>     .p.flags       = AVFILTER_FLAG_METADATA_ONLY,
>     FILTER_INPUTS(ff_video_default_filterpad),
>     FILTER_OUTPUTS(ff_video_default_filterpad),
> };
>
> const FFFilter ff_vf_foo = {
>     .p.name        = "foo",
>     .p.description = NULL_IF_CONFIG_SMALL("Another foo filter"),
>     .p.flags       = AVFILTER_FLAG_METADATA_ONLY,
>     FILTER_INPUTS(ff_video_default_filterpad),
>     FILTER_OUTPUTS(ff_video_default_filterpad),
> };
> ```
>
> Then, from the ffmpeg source tree, run configure specifying where the
> extra filter is located:
>
> ```
> ./configure --extra-filter=/tmp/my-shiny-filter
> make ffplay
> ```
>
> Now you can use the filters:
>
> ```
> ./ffplay /path/to/file.webm -vf 'foo,baz'
> ```
>
> What works:
>
> - Building C based filters with no extra dependencies.
> - Multiple filters in the same object file.
>
> What does not work:
>
> - The extra filters will not use the same CC flags used to build the
>   built-in filters as I could get it to work yet.
> - Due to the above limitation, you cannot include headers of extra
>   dependencies, for instance, `json.h` in the example.
> - You can pass arbitrary CFLAGS or LDFLAGS in the filter.json file,
>   but they should be passed only then building/linking `libavfilter`,
>   instead of other libraries.
>
> What was not implemented:
>
> - I believe it would be useful to check if the license of the filter is
>   compatible with the license used to build FFmpeg.
> - Only extra filters written in C (maybe C++?) are supported for now.
>   One of my goals is to enable Rust as well.
>
> Signed-off-by: Leandro Santiago <leandrosansilva@gmail.com>
> ---
>  .gitignore               |  3 ++
>  configure                | 61 ++++++++++++++++++++++++++++++++++++++++
>  libavfilter/Makefile     |  4 +++
>  libavfilter/allfilters.c |  1 +
>  4 files changed, 69 insertions(+)
>
> diff --git a/.gitignore b/.gitignore
> index 9cfc78b414..4963e90191 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -43,3 +43,6 @@
>  /tools/python/__pycache__/
>  /libavcodec/vulkan/*.c
>  /libavfilter/vulkan/*.c
> +/ffbuild/extra-filters.txt
> +/ffbuild/extra-filters.mak
> +/libavfilter/extra_filters_extern.h
> diff --git a/configure b/configure
> index 750c99e3b9..6a2adc6c05 100755
> --- a/configure
> +++ b/configure
> @@ -179,6 +179,7 @@ Individual component options:
>    --enable-filter=NAME     enable filter NAME
>    --disable-filter=NAME    disable filter NAME
>    --disable-filters        disable all filters
> +  --extra-filter=/foo/bar  add extra filter from directory. This option can be used multiple times
>  
>  External library support:
>  
> @@ -1798,6 +1799,7 @@ AVDEVICE_COMPONENTS="
>  
>  AVFILTER_COMPONENTS="
>      filters
> +    extra_filters
>  "
>  
>  AVFORMAT_COMPONENTS="
> @@ -4382,6 +4384,8 @@ do_random(){
>      $action $(rand_list "$@" | awk "BEGIN { srand($random_seed) } \$1 == \"prob\" { prob = \$2; next } rand() < prob { print }")
>  }
>  
> +rm -f ffbuild/extra-filters.txt
> +
>  # deprecated components (disabled by default)
>  disable sonic_encoder sonic_ls_encoder
>  
> @@ -4457,6 +4461,10 @@ for opt do
>                  die_unknown $opt
>              fi
>          ;;
> +        --extra-filter=*)
> +            filter_path="${opt#--extra-filter=}"
> +            echo "$filter_path" >> ffbuild/extra-filters.txt
> +        ;;
>          --list-*)
>              NAME="${opt#--list-}"
>              is_in $NAME $COMPONENT_LIST || die_unknown $opt
> @@ -4487,6 +4495,36 @@ for opt do
>      esac
>  done
>  
> +find_extra_filters_extern() {
> +  # TODO: handle invalid filter
> +  while read f; do
> +    jq -r '.symbols[]' < "$f/filter.json" | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]_]\{1,\}\)/\1_filter/'
> +  done < ffbuild/extra-filters.txt
> +}
> +
> +EXTRA_FILTER_LIST=$(find_extra_filters_extern)
> +
> +for n in extra_filters; do
> +    v=$(toupper ${n%s})_LIST
> +    eval enable \$$v
> +    eval ${n}_if_any="\$$v"
> +done
> +
> +FILTER_LIST="
> +    $FILTER_LIST
> +    $EXTRA_FILTER_LIST
> +"
> +
> +AVFILTER_COMPONENTS_LIST="
> +    $AVFILTER_COMPONENTS_LIST
> +    $EXTRA_FILTER_LIST
> +"
> +
> +ALL_COMPONENTS="
> +    $ALL_COMPONENTS
> +    $EXTRA_FILTER_LIST
> +"
> +
>  for e in $env; do
>      eval "export $e"
>  done
> @@ -7165,6 +7203,10 @@ enabled rkmpp             && { require_pkg_config rkmpp rockchip_mpp  rockchip/r
>                               }
>  enabled vapoursynth       && require_headers "vapoursynth/VSScript4.h vapoursynth/VapourSynth4.h"
>  
> +while read f; do
> +  # NOTE: this eval is dangerous, as it allows arbitrary code execution!
> +  eval $(jq -r '.check // true' < "$f/filter.json")
> +done < ffbuild/extra-filters.txt
>  
>  if enabled gcrypt; then
>      GCRYPT_CONFIG="${cross_prefix}libgcrypt-config"
> @@ -8243,6 +8285,12 @@ for entry in $LIBRARY_LIST $PROGRAM_LIST $EXTRALIBS_LIST; do
>      eval echo "EXTRALIBS-${entry}=\$${entry}_extralibs" >> ffbuild/config.mak
>  done
>  
> +echo "" > ffbuild/extra-filters.mak
> +
> +while read f; do
> +    echo "include $f/filter.mak" >> ffbuild/extra-filters.mak
> +done < ffbuild/extra-filters.txt
> +
>  cat > $TMPH <<EOF
>  /* Automatically generated by configure - do not modify! */
>  #ifndef FFMPEG_CONFIG_H
> @@ -8330,6 +8378,19 @@ cp_if_changed $TMPH libavutil/avconfig.h
>  # ...
>  eval "$(sed -n "s/^extern const FFFilter ff_\([avfsinkrc]\{2,5\}\)_\(.*\);/full_filter_name_\2=\1_\2/p" $source_path/libavfilter/allfilters.c)"
>  
> +rm -f libavfilter/extra_filters_extern.h
> +
> +# Handle extra filters
> +while read f; do
> +    eval "$(jq -r '.symbols[]' < "$f/filter.json" | sed 's/^ff_\([avfsinkrc]\{2,5\}\)_\([[:alnum:]]\{1,\}\)$/full_filter_name_\2=\1_\2/')"
> +    jq -r '.symbols[]' < "$f/filter.json" | while read symbol; do
> +      echo "extern const FFFilter $symbol;" >> libavfilter/extra_filters_extern.h
> +      echo "EXTRA_FILTER_$(echo $symbol | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]]\{1,\}\)$/\1/' | tr a-z A-Z)_LOCATION = $f" >> ffbuild/extra-filters.mak
> +      echo "LDFLAGS += $(jq -r '.ldflags // ""' < "$f/filter.json")" >> ffbuild/extra-filters.mak
> +      echo "CFLAGS += $(jq -r '.cflags // ""' < "$f/filter.json")" >> ffbuild/extra-filters.mak
> +    done
> +done < ffbuild/extra-filters.txt
> +
>  # generate the lists of enabled components
>  print_enabled_components(){
>      file=$1
> diff --git a/libavfilter/Makefile b/libavfilter/Makefile
> index 7c0d879ec9..9b22aece3a 100644
> --- a/libavfilter/Makefile
> +++ b/libavfilter/Makefile
> @@ -27,6 +27,10 @@ OBJS = allfilters.o                                                     \
>  include $(SRC_PATH)/libavfilter/dnn/Makefile
>  include $(SRC_PATH)/libavfilter/vulkan/Makefile
>  
> +# extra filters handling
> +include $(SRC_PATH)/ffbuild/extra-filters.mak
> +EXTRA_FILTER_FLAGS = -I$(PWD) -I$(PWD)/libavfilter $(CPPFLAGS) $(CC_DEPFLAGS)
> +
>  OBJS-$(HAVE_LIBC_MSVCRT)                     += file_open.o
>  OBJS-$(HAVE_THREADS)                         += pthread.o
>  
> diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
> index 740d9ab265..e8565de5b0 100644
> --- a/libavfilter/allfilters.c
> +++ b/libavfilter/allfilters.c
> @@ -621,6 +621,7 @@ extern  const FFFilter ff_vsrc_buffer;
>  extern  const FFFilter ff_asink_abuffer;
>  extern  const FFFilter ff_vsink_buffer;
>  
> +#include "libavfilter/extra_filters_extern.h"
>  #include "libavfilter/filter_list.c"
>  
>  
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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 1199 bytes --]

Hi

On Thu, Mar 13, 2025 at 01:18:49PM +0100, Leandro Santiago wrote:
> This is a POC/prototype that aims to enable out of tree filters on
> FFmpeg.
> 
> Here I name them "extra filters".
> 

> It introduces the program `jq` as a new build dependency.

I dont think this dependency is needed to achieve linking to filters
in another directory
i think its worth the few hours extra time to find a clean/nice way to do it
with no new depeandancies

also there is the quite intriguing option of using "git merge" to include
external filters
What i mean here is that there could be a script lets call it ffmerge

"ffmerge available" would check some online repository and list whats
compatible with the current checkout

"ffmerge merge shiny_filter" would then merge the shiny filter repository/branch

Advanatge would be that this is more powerfull than just linking external
filters.
Disadvantage is that for this to work care needs to be taken that conflicts
do not occur

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is dangerous to be right in matters on which the established authorities
are wrong. -- Voltaire

[-- Attachment #1.2: signature.asc --]
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[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Leandro Santiago]

On 3/14/25 16:04, Michael Niedermayer wrote:
> Hi
>
> On Thu, Mar 13, 2025 at 01:18:49PM +0100, Leandro Santiago wrote:
>> This is a POC/prototype that aims to enable out of tree filters on
>> FFmpeg.
>>
>> Here I name them "extra filters".
>>
Thinking now, "extra filters" is not a good name. Maybe "external" or "oot"
>> It introduces the program `jq` as a new build dependency.
> I dont think this dependency is needed to achieve linking to filters
> in another directory
To make it clear, the "extra filters" are linked in the same way the 
current filters are: direct as part libavfilter.(so|a). They are not 
dynamically linked.
> i think its worth the few hours extra time to find a clean/nice way to do it
> with no new depeandancies

I used json as a quick way to define the filter metadata (thus the usage 
of JQ to query them), but I confess it could have been any other format. 
I used json to get the proof of concept done :-)

Ideally it would be written in a native format to the build system, if 
something like CMake or Meson was being used.

Maybe the metadata could even be in a Makefile or spread over multiple 
files with no structure. The use of json was for pure convenience. Would 
you have any format to suggest? Is there anything similar in the 
codebase I could have a look at?

This is an example of metadata file at the moment:

{
"ldflags":"-ljson-c",
"cflags":"-DFOO=234",
"check":"require_pkg_config json json-c json-c/json.h json_c_version_num",
"symbols":["ff_vf_foo","ff_vf_bar"]
}

A simpler way to represent it would be put each field in a different 
pure text file, for instance:

symbols.txt:

ff_vf_foo ff_vf_bar

The most important aspect here is that the filter metadata (symbols, 
names, flags) need to be in a format easy to parse from the `configure` 
script.

I did some improvements on my patch and I managed to get the filter to 
pass extra flags on building.

Although the use of forgejo is not yet official, I am keeping my changes 
on it for now, as I still struggle with the email workflow:

https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/13

The "example" filter can be found at:

https://gitlab.com/leandrosansilva/ffmpeg-extra-filter-example/

To use it, simply clone this repo and build ffmpeg with 
`--extra-filter=/path/to/ffmpeg-extra-filter-example`.

>
> also there is the quite intriguing option of using "git merge" to include
> external filters
> What i mean here is that there could be a script lets call it ffmerge
How would it work when using release tarballs, without git?
> "ffmerge available" would check some online repository and list whats
> compatible with the current checkout
>
> "ffmerge merge shiny_filter" would then merge the shiny filter repository/branch
Wouldn't it put more burden over the devs to maintain such 
catalog/repository and the tooling around it? I am fine with that, I 
just wonder how the community would accept it. Having no filter 
catalog/repo feels to be the simplest step one could take at the moment.
>
> Advanatge would be that this is more powerfull than just linking external
> filters.
> Disadvantage is that for this to work care needs to be taken that conflicts
> do not occur

I see that simply keeping the filter outside and linking them at build 
time put almost no burden on the ffmpeg devs.

As, provided there is no promise of a stable API, it's up to the 
developers of the "extra" filters to make their filters build.

>
> thx
>
> [...]
>
>
> _______________________________________________
> ffmpeg-devel mailing list
> ffmpeg-devel@ffmpeg.org
> https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>
> To unsubscribe, visit link above, or email
> ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".
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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 1408 bytes --]

On Fri, Mar 14, 2025 at 05:13:23PM +0100, Leandro Santiago wrote:
[...]
> > 
> > also there is the quite intriguing option of using "git merge" to include
> > external filters
> > What i mean here is that there could be a script lets call it ffmerge

> How would it work when using release tarballs, without git?

it would tell the user to run it in a git checkout or an empty directory.
The script would already have the ability to merge external filter repos
so also pulling mainline is no real extra complexity


> > "ffmerge available" would check some online repository and list whats
> > compatible with the current checkout
> > 
> > "ffmerge merge shiny_filter" would then merge the shiny filter repository/branch

> Wouldn't it put more burden over the devs to maintain such
> catalog/repository and the tooling around it? I am fine with that, I just
> wonder how the community would accept it. Having no filter catalog/repo
> feels to be the simplest step one could take at the moment.

theres no need for such catalog. I just think that if external filter
support is added, that someone will then likely start maintaining a catalog
of these filters.


thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Good people do not need laws to tell them to act responsibly, while bad
people will find a way around the laws. -- Plato

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[-- Attachment #2: Type: text/plain, Size: 251 bytes --]

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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Lynne]

On 13/03/2025 13:18, Leandro Santiago wrote:
> This is a POC/prototype that aims to enable out of tree filters on
> FFmpeg.
> 
> Here I name them "extra filters".
> 
> It introduces the program `jq` as a new build dependency.
> 
> To test it, create a directory, for instance, /tmp/my-shiny-filter/ and
> inside it, create the following files:
> 
> `filter.json`, with the content:

This is a pointless patch and a pointlessly complex addition to the 
build system. I wouldn't accept something like this.
Those who for some reason have custom filters simply distribute their 
own branch with properly integrated filters. This also lets them 
upstream it if they want to.
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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Nicolas George]

Lynne (HE12025-03-14):
> This is a pointless patch and a pointlessly complex addition to the build
> system. I wouldn't accept something like this.
> Those who for some reason have custom filters simply distribute their own
> branch with properly integrated filters.

That works for third-party from one third-party. This feature helps
users who want to use filters from multiple third-party. With what you
describe, they would have to merge the branches, which might not be
trivial.

On the other hand, the JSON in this makes it look like it was designed
by looking at how fashionable languages NIHed their own f5g package
system.

If instead it was designed by asking “what would a ffmpeg developer do”,
it would just have configure run ext/*/configure and then Makefile
include $(CONFIG_EXT_WHATEVER).

Regards,

-- 
  Nicolas George
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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Leandro Santiago]

On 3/14/25 19:21, Nicolas George wrote:
> Lynne (HE12025-03-14):
>> This is a pointless patch and a pointlessly complex addition to the build
>> system. I wouldn't accept something like this.
>> Those who for some reason have custom filters simply distribute their own
>> branch with properly integrated filters.
> That works for third-party from one third-party. This feature helps
> users who want to use filters from multiple third-party. With what you
> describe, they would have to merge the branches, which might not be
> trivial.
>
> On the other hand, the JSON in this makes it look like it was designed
> by looking at how fashionable languages NIHed their own f5g package
> system.

Thx for the review and to make it clear:

it was not my intention to suggest my implementation (using json and so 
on) as the final one or to be mainlined.

I notice now my lack of netiquette, as it seems I was not clear on 
saying that this is a proof of concept (POC, in the subject): I wanted 
to try something (support for non mainlined filters), and wanted to 
check whether that was possible or not, and finally get feedback.

Using json+jq was the quickest, dirtiest way to accomplished that.

I personally conclude that the POC was successful: I managed to get a 
new filter, not mainlined, to be built into ffmpeg. Next steps would be 
throw the code away and implement it properly

Obviously I need the agreement from you experienced ffmpeg devs for such 
conclusion.

I should probably have called it a RFC or similar. My mistake. I still 
struggle with using the mailing list contribution model, as in a PR/MR 
model I would simply keep a WIP request until it gets to a good shape. 
With the ML model, I feel doing so is very error prone, but this is 
probably my lack of experience with it.

My goal now is to know whether there is any interest from the ffmpeg 
devs on having such feature (regardless of the implementation), as there 
seems to be lots of disagreement.

I am personally interested on it, due to the fact I am writing a filter 
in Rust that is very unlikely to ever me mainlined. Right now I need to 
constantly rebase branches, but I'd be way happier if I could simply 
rely on some "official" support in the ffmpeg codebase to use it.

Another benefit could be moving out some filters that are "not very 
loved" or that tend to "get rotten". My impression/opinion is that the 
DNN stuff could very well be moved out, to evolve independently from the 
main ffmpeg repo. I totally respect the developers who worked on it, to 
be very clear. I benefit from the DNN code and want to keep it working well.

>
> If instead it was designed by asking “what would a ffmpeg developer do”,
> it would just have configure run ext/*/configure and then Makefile
> include $(CONFIG_EXT_WHATEVER).

Thank you for the feedback. I requested some thoughts on the topic a few 
days ago [1], and I see that probably the message was not clear.

I find this `simply run ext/configure approach` interesting and will 
have a look at it and later let you know my findings.

[1] https://ffmpeg.org/pipermail/ffmpeg-devel/2025-March/340895.html

>
> Regards,
>
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Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree filters

[Soft Works]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Lynne
> Sent: Freitag, 14. März 2025 17:58
> To: ffmpeg-devel@ffmpeg.org
> Subject: Re: [FFmpeg-devel] [PATCH] avfilter: POC: enable out-of-tree
> filters
> 
> On 13/03/2025 13:18, Leandro Santiago wrote:
> > This is a POC/prototype that aims to enable out of tree filters on
> > FFmpeg.
> >
> > Here I name them "extra filters".
> >
> > It introduces the program `jq` as a new build dependency.
> >
> > To test it, create a directory, for instance, /tmp/my-shiny-filter/
> and
> > inside it, create the following files:
> >
> > `filter.json`, with the content:
> 
> This is a pointless patch and a pointlessly complex addition to the
> build system. I wouldn't accept something like this.
> Those who for some reason have custom filters simply distribute their
> own branch with properly integrated filters. This also lets them
> upstream it if they want to.
> _______________________________________________

Hi Lynne,

as someone who is using a number of custom filters, I can say that the "own branch with properly integrated filters" approach is a continuing source of trouble when rebasing or trying to apply it to different base branches. Even though these aren't really 3rd party filters, having a mechanism for it would make it much easier to maintain additional filters.
I don't want to argue about the specific approach as other will know better than me, but I'm sure that it's possible to find a nice non-complex way, no?

sw




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Re: [FFmpeg-devel] [PATCH] avfilter: Proof of Concept: enable out-of-tree filters

[Leandro Santiago]

[-- Attachment #1: Type: text/plain, Size: 6921 bytes --]

I've applied a few changes from your feedback, the following is how the feature looks like.

***Disclaimer***

this is still a proof of concept and for now I am looking for your feedback and help. There are lots of rough corners and stuff that does not work. I by no means intend to request the changes as they are to be merged. Call it an RFC if you will.

Also, I am not sending the patch as an attachment, and leave the e-mail body for discussion only. I am not sure whether this is a good approach or goes against the mailing list policy. This is the time I wish we could really contribute using the Pull Request more on a nice web interface.

If you folks want to experiment, I pushed my changes in this PR: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/13

***Finish disclaimer***

I changed the name convention from "extra filters" to "external filters", as it sounds more natural. (Another possibility would be "extension filters", so please let me know what you think).

The build system will automatically pick up any filters in the subdirectory `ext/libavfilter`, and ignore it if it does not exist.

The rationale behind this directory structure is to reserve the possibility of extensions of other libraries as well.

An external filter is composed by at least one Makefile, and this Makefile has some "metadata" encoded in its comments, used by the `./configure` script to generate some code. I'll show how they look like in an example.

Although this way to encode metadata looks very ugly and I am pretty sure can be improved, this is the best I could for now, and I hope you folks can point me directions on how to improve it, as you have more knowledge of the build system than I do.

Here are the metadata types:

- check: this is a command used to check if 3rd party dependencies are available and enabling them within the build system. The command here is executed by `./configure`. This entry is optional and for now there can be only one of them, due to technical limitations of my implementation.

- symbol: this entry can appear multiple times, and indicates the name of the FFFilter objects exported by the filter. There must be one entry per exported symbol. These entries are used by `./configure` to generate the list of enabled filters.

- ldflags: those are extra LDFLAGS to be used to link libavfilter. I am not happy this this one at all, as such information ideally should be encoded as Makefile variables, but I confess I could not manage to do it. I'd be happy to get directions on where in the build system to look for the right "hook", but I'll continue looking for it as well.

As an example, here is how one can create an empty filter. Just to exercise the build system, the example filter depends on an external library, json-c, which is found using pkg-config and will be dynamically linked to libavfilter. In case json-c is not found, `./configure` will fail, as expected.

```

mkdir -p ext/libavfilter/example

```

Then create the a file ext/libavfilter/example/Makefile with the content:

```

# check: require_pkg_config json json-c json-c/json.h json_c_version_num
# symbol: ff_vf_example
# ldflags: -ljson-c

OBJS += vf_example.o
CFLAGS += -DFOO=1234

libavfilter/vf_example.o:
        $(CC) $(EXTERNAL_FILTER_FLAGS) $(CPPFLAGS) $(CFLAGS) -c -o $@ $(EXTERNAL_FILTER_EXAMPLE_LOCATION)/vf_example.c

```

Then, create the file ext/libavfilter/example/Makefile/vf_example.c with the content:


```

#include "libavutil/internal.h"
#include "avfilter.h"
#include "filters.h"
#include "video.h"

#include <json.h>

static int process_command(AVFilterContext *ctx, const char *cmd, const char *args, char *res, int res_len, int flags) {
  // NOTE: I know this makes no sense, I just wanted to use some symbol from json-c
  // in a way the compiler cannot optimize it out
  return json_c_version_num();
}


const FFFilter ff_vf_example = {
    .p.name        = "example",
    .p.description = NULL_IF_CONFIG_SMALL("An external example filter"),
    .p.flags       = AVFILTER_FLAG_METADATA_ONLY,
    FILTER_INPUTS(ff_video_default_filterpad),
    FILTER_OUTPUTS(ff_video_default_filterpad),
    .process_command = process_command,
};

```

(You can skip this manually creating those files by checking out this example filter from gitlab: https://gitlab.com/leandrosansilva/ffmpeg-extra-filter-example)

Now you can compile ffmpeg as usual, with `./configure && make && make install` and use the filter.

In my tests, building ffmpeg libraries either in static and shared mode work, with the extra dependencies properly linked.


Explanation:

- The .o files for the external filters will be generated in the same place as the built-in filters, in libavfilter/. That means that two external filters cannot generate the same .o files.

- A new variable with the format EXTERNAL_FILTER_$(FILTER_SYMBOL_IN_UPPERCASE)_LOCATION will be generated for each FFFilter exported. More explanation about that below.

- The build system offers now a variable `EXTERNAL_FILTER_FLAGS` which adds the paths of the libavfilter private headers to the compiler when building the external filters. The idea here is for code for an external filter to look exactly as if it was a built-in filter: the include paths should be the same. This will make it easier for external filters to be moved as built-in and the other way around, not requiring much code changes.


TODO:

- Find a way to remove the `ldflags` metadata entry to turn it into a Makefile variable.

- Allow multiple `check` metadata entries, to make it easier to check for multiple 3rd party dependencies.

- Better error handling on malformed/invalid filter metadata.

- Find a way to encode conditional builds in the metadata. I am here thinking on filters like the `dnn` family, which can have multiple backends, which are now chosen using `--enable-openvino`, `--enable-libtorch`, `--enable-libtensorflow` or the drawtext filter that has optional dependencies. Maybe the external filters could hook new `--enable-*` options to `./configure`, but this smells like trouble when multiple filters specify the same optional dependencies.

- You can see in the example Makefile that a new "magical" variable named `EXTERNAL_FILTER_EXAMPLE_LOCATION` was created by the build system. It looks ugly to me, but I could not find a way to obtain the path of the current Makefile via make, and I needed a way to specify the path of the filter source files. If you know a cleaner way to do it, please let me know.

- Make it possible to link filters written in other languages. My "final" goal for is Rust, but it should not prevent the use of C++ or Zig, for instance. I believe this can be done in a further iteration. For now my focus is only supporting C.

- Once the implementation and "spec" is agreed, document it.

- Refactor the changes in the build system to improve legibility.


Regards,

Leandro

[-- Attachment #2: 0001-avfilter-Proof-of-Concept-enable-out-of-tree-filters.patch --]
[-- Type: text/x-patch, Size: 7179 bytes --]

From 7486f878b982867667892611e181dc4eab3298c8 Mon Sep 17 00:00:00 2001
From: Leandro Santiago <leandrosansilva@gmail.com>
Date: Wed, 12 Mar 2025 13:42:42 +0100
Subject: [PATCH] avfilter: Proof of Concept: enable out-of-tree filters

This is a POC/prototype that aims to enable out of tree filters on
FFmpeg.

Here is how to test it, with an example filter:

```
mkdir -p ext/libavfilter
pushd ext/libavfilter
git clone https://gitlab.com/leandrosansilva/ffmpeg-extra-filter-example example
popd
```

Then compile ffmpeg as usual:

```
./configure && make && make install
```

Now you can use the filters:

```
ffplay /path/to/file.webm -vf 'foo,bar'
```

What works:

- Building C based filters with no extra, or simple dependencies.
- Multiple filters in the same object file.

What is ugly:

- The filter metadata is hidden in the Makefile comments, and this is
  needed because at `./configure` time, executed before make, some code
  needs to be generated and, although such generation could in theory be
  done via make, this feels like too much change at the moment.

- Among the metadata, there are linker and compiler flags, which would
  look much better if they were simple make variables.

- At the moment it's possible for only one `check` metadata entry to be
  included in the Makefile, but we should support multiple of them, for
  the case when there are multiple extra dependencies.

What was not implemented:

- I believe it would be useful to check if the license of the filter is
  compatible with the license used to build FFmpeg.

- Only extra filters written in C (maybe C++?) are supported for now.
  One of my goals is to enable Rust as well.

- There should be a way to have optional dependencies, for filters that
  can have multiple "backends", for instance, to be chosen at build time.

Signed-off-by: Leandro Santiago <leandrosansilva@gmail.com>
---
 .gitignore               |  4 +++
 configure                | 75 ++++++++++++++++++++++++++++++++++++++++
 libavfilter/Makefile     |  4 +++
 libavfilter/allfilters.c |  1 +
 4 files changed, 84 insertions(+)

diff --git a/.gitignore b/.gitignore
index 430abaf91b..4eae911379 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,3 +44,7 @@
 /tools/python/__pycache__/
 /libavcodec/vulkan/*.c
 /libavfilter/vulkan/*.c
+/ffbuild/external-filters.txt
+/ffbuild/external-filters.mak
+/libavfilter/external_filters_extern.h
+/ext
diff --git a/configure b/configure
index d84e32196d..f7bb2cc38a 100755
--- a/configure
+++ b/configure
@@ -1798,6 +1798,7 @@ AVDEVICE_COMPONENTS="
 
 AVFILTER_COMPONENTS="
     filters
+    external_filters
 "
 
 AVFORMAT_COMPONENTS="
@@ -4489,6 +4490,50 @@ for opt do
     esac
 done
 
+symbols_from_external_filter_makefile() {
+  grep '^#.*symbol:' < "$1" | sed -e 's|#\s*symbol: \(.*\)|\1|g'
+}
+
+list_external_filter_makefiles() {
+  [ ! -d "ext/libavfilter" ] && return
+
+  for f in ext/libavfilter/*; do
+    [ -f "$f/Makefile" ] && echo $f/Makefile
+  done
+}
+
+list_external_filter_makefiles > ffbuild/external-filters.txt
+
+find_external_filters_extern() {
+  # TODO: handle invalid filter
+  while read Makefile; do
+    symbols_from_external_filter_makefile "$Makefile" | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]_]\{1,\}\)/\1_filter/'
+  done < ffbuild/external-filters.txt
+}
+
+EXTERNAL_FILTER_LIST=$(find_external_filters_extern)
+
+for n in external_filters; do
+    v=$(toupper ${n%s})_LIST
+    eval enable \$$v
+    eval ${n}_if_any="\$$v"
+done
+
+FILTER_LIST="
+    $FILTER_LIST
+    $EXTERNAL_FILTER_LIST
+"
+
+AVFILTER_COMPONENTS_LIST="
+    $AVFILTER_COMPONENTS_LIST
+    $EXTERNAL_FILTER_LIST
+"
+
+ALL_COMPONENTS="
+    $ALL_COMPONENTS
+    $EXTERNAL_FILTER_LIST
+"
+
 for e in $env; do
     eval "export $e"
 done
@@ -7173,6 +7218,11 @@ enabled rkmpp             && { require_pkg_config rkmpp rockchip_mpp  rockchip/r
                              }
 enabled vapoursynth       && require_headers "vapoursynth/VSScript4.h vapoursynth/VapourSynth4.h"
 
+# Check for the dependencies of the external filters
+while read Makefile; do
+  # NOTE: this eval is dangerous, as it allows arbitrary code execution!
+  eval $(grep '^#.*check:' "$Makefile" | sed 's|#\s*check: \(.*\)|\1|g')
+done < ffbuild/external-filters.txt
 
 if enabled gcrypt; then
     GCRYPT_CONFIG="${cross_prefix}libgcrypt-config"
@@ -8250,12 +8300,23 @@ IGNORE_TESTS=$ignore_tests
 VERSION_TRACKING=$version_tracking
 EOF
 
+while read Makefile; do
+  # NOTE: this eval is dangerous, as it allows arbitrary code execution!
+  eval "avfilter_extralibs=\"\$avfilter_extralibs $(grep '^#.*ldflags:' "$Makefile" | sed 's|#\s*ldflags: \(.*\)|\1|g')\""
+done < ffbuild/external-filters.txt
+
 map 'eval echo "${v}_FFLIBS=\$${v}_deps" >> ffbuild/config.mak' $LIBRARY_LIST
 
 for entry in $LIBRARY_LIST $PROGRAM_LIST $EXTRALIBS_LIST; do
     eval echo "EXTRALIBS-${entry}=\$${entry}_extralibs" >> ffbuild/config.mak
 done
 
+echo "" > ffbuild/external-filters.mak
+
+while read Makefile; do
+    echo "include $Makefile" >> ffbuild/external-filters.mak
+done < ffbuild/external-filters.txt
+
 cat > $TMPH <<EOF
 /* Automatically generated by configure - do not modify! */
 #ifndef FFMPEG_CONFIG_H
@@ -8343,6 +8404,20 @@ cp_if_changed $TMPH libavutil/avconfig.h
 # ...
 eval "$(sed -n "s/^extern const FFFilter ff_\([avfsinkrc]\{2,5\}\)_\(.*\);/full_filter_name_\2=\1_\2/p" $source_path/libavfilter/allfilters.c)"
 
+rm -f libavfilter/external_filters_extern.h
+
+# register the symbols of the external filters
+while read Makefile; do
+    eval "$(symbols_from_external_filter_makefile "$Makefile" \
+      | sed 's/^ff_\([avfsinkrc]\{2,5\}\)_\([[:alnum:]]\{1,\}\)$/full_filter_name_\2=\1_\2/')"
+
+    symbols_from_external_filter_makefile "$Makefile" | while read symbol; do
+        echo "extern const FFFilter $symbol;" >> libavfilter/external_filters_extern.h
+        echo "EXTERNAL_FILTER_$(echo $symbol | sed 's/^ff_[avfsinkrc]\{2,5\}_\([[:alnum:]]\{1,\}\)$/\1/' | tr a-z A-Z)_LOCATION = $f" \
+            >> ffbuild/external-filters.mak
+    done
+done < ffbuild/external-filters.txt
+
 # generate the lists of enabled components
 print_enabled_components(){
     file=$1
diff --git a/libavfilter/Makefile b/libavfilter/Makefile
index 7c0d879ec9..877b24c30f 100644
--- a/libavfilter/Makefile
+++ b/libavfilter/Makefile
@@ -27,6 +27,10 @@ OBJS = allfilters.o                                                     \
 include $(SRC_PATH)/libavfilter/dnn/Makefile
 include $(SRC_PATH)/libavfilter/vulkan/Makefile
 
+# external filters handling
+include $(SRC_PATH)/ffbuild/external-filters.mak
+EXTERNAL_FILTER_FLAGS = -I$(PWD) -I$(PWD)/libavfilter
+
 OBJS-$(HAVE_LIBC_MSVCRT)                     += file_open.o
 OBJS-$(HAVE_THREADS)                         += pthread.o
 
diff --git a/libavfilter/allfilters.c b/libavfilter/allfilters.c
index 740d9ab265..c2d576e4be 100644
--- a/libavfilter/allfilters.c
+++ b/libavfilter/allfilters.c
@@ -621,6 +621,7 @@ extern  const FFFilter ff_vsrc_buffer;
 extern  const FFFilter ff_asink_abuffer;
 extern  const FFFilter ff_vsink_buffer;
 
+#include "libavfilter/external_filters_extern.h"
 #include "libavfilter/filter_list.c"
 
 
-- 
2.48.1


[-- Attachment #3: Type: text/plain, Size: 251 bytes --]

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