[FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[Zhao Zhili]

From: Zhao Zhili <zhilizhao@tencent.com>

---
 libavformat/avformat.h | 3 +--
 libavformat/format.c   | 2 ++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 2034d2aecc..6edcf11022 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -470,8 +470,7 @@ typedef struct AVProbeData {
 /**
  * The muxer/demuxer is experimental and should be used with caution.
  *
- * - demuxers: will not be selected automatically by probing, must be specified
- *             explicitly.
+ * Will not be selected automatically, must be specified explicitly.
  */
 #define AVFMT_EXPERIMENTAL  0x0004
 #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
diff --git a/libavformat/format.c b/libavformat/format.c
index 71018ea6ab..516925e7e4 100644
--- a/libavformat/format.c
+++ b/libavformat/format.c
@@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
     /* Find the proper file type. */
     score_max = 0;
     while ((fmt = av_muxer_iterate(&i))) {
+        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
+            continue;
         score = 0;
         if (fmt->name && short_name && av_match_name(short_name, fmt->name))
             score += 100;
-- 
2.46.0

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Re: [FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[James Almer]

[-- Attachment #1.1.1: Type: text/plain, Size: 1536 bytes --]

On 6/5/2025 1:06 PM, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> ---
>   libavformat/avformat.h | 3 +--
>   libavformat/format.c   | 2 ++
>   2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index 2034d2aecc..6edcf11022 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -470,8 +470,7 @@ typedef struct AVProbeData {
>   /**
>    * The muxer/demuxer is experimental and should be used with caution.
>    *
> - * - demuxers: will not be selected automatically by probing, must be specified
> - *             explicitly.
> + * Will not be selected automatically, must be specified explicitly.

"It will not be selected automatically, and must be specified explicitly."

>    */
>   #define AVFMT_EXPERIMENTAL  0x0004
>   #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
> diff --git a/libavformat/format.c b/libavformat/format.c
> index 71018ea6ab..516925e7e4 100644
> --- a/libavformat/format.c
> +++ b/libavformat/format.c
> @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
>       /* Find the proper file type. */
>       score_max = 0;
>       while ((fmt = av_muxer_iterate(&i))) {
> +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
> +            continue;
>           score = 0;
>           if (fmt->name && short_name && av_match_name(short_name, fmt->name))
>               score += 100;


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Re: [FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[Zhao Zhili]

> On Jun 6, 2025, at 00:09, James Almer <jamrial@gmail.com> wrote:
> 
> On 6/5/2025 1:06 PM, Zhao Zhili wrote:
>> From: Zhao Zhili <zhilizhao@tencent.com>
>> ---
>>  libavformat/avformat.h | 3 +--
>>  libavformat/format.c   | 2 ++
>>  2 files changed, 3 insertions(+), 2 deletions(-)
>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>> index 2034d2aecc..6edcf11022 100644
>> --- a/libavformat/avformat.h
>> +++ b/libavformat/avformat.h
>> @@ -470,8 +470,7 @@ typedef struct AVProbeData {
>>  /**
>>   * The muxer/demuxer is experimental and should be used with caution.
>>   *
>> - * - demuxers: will not be selected automatically by probing, must be specified
>> - *             explicitly.
>> + * Will not be selected automatically, must be specified explicitly.
> 
> "It will not be selected automatically, and must be specified explicitly."

OK.

I have another question. The AVFMT_EXPERIMENTAL flag is different from
AV_CODEC_CAP_EXPERIMENTAL, that AVFMT_EXPERIMENTALl flag
doesn’t check against strict_std_compliance. It’s kind of overlap for these
two flags.

There are practical reasons, like the AVFMT_EXPERIMENTAL need to check
early. And when user specify the demuxer/muxer explicitly, it make sense to
skip the check.

So, when WHIP add AVFMT_EXPERIMENTAL flag, it has no real effect since
WHIP is always specified explicitly, except user can check and see the flag.

> 
>>   */
>>  #define AVFMT_EXPERIMENTAL  0x0004
>>  #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
>> diff --git a/libavformat/format.c b/libavformat/format.c
>> index 71018ea6ab..516925e7e4 100644
>> --- a/libavformat/format.c
>> +++ b/libavformat/format.c
>> @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
>>      /* Find the proper file type. */
>>      score_max = 0;
>>      while ((fmt = av_muxer_iterate(&i))) {
>> +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
>> +            continue;
>>          score = 0;
>>          if (fmt->name && short_name && av_match_name(short_name, fmt->name))
>>              score += 100;
> 
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> 

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[FFmpeg-devel] [PATCH v2] avformat/format: make experimental flag works for muxer

[Zhao Zhili]

From: Zhao Zhili <zhilizhao@tencent.com>

---
 libavformat/avformat.h | 3 +--
 libavformat/format.c   | 2 ++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index 2034d2aecc..441e31bc2f 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -470,8 +470,7 @@ typedef struct AVProbeData {
 /**
  * The muxer/demuxer is experimental and should be used with caution.
  *
- * - demuxers: will not be selected automatically by probing, must be specified
- *             explicitly.
+ * It will not be selected automatically, and must be specified explicitly.
  */
 #define AVFMT_EXPERIMENTAL  0x0004
 #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
diff --git a/libavformat/format.c b/libavformat/format.c
index 71018ea6ab..516925e7e4 100644
--- a/libavformat/format.c
+++ b/libavformat/format.c
@@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
     /* Find the proper file type. */
     score_max = 0;
     while ((fmt = av_muxer_iterate(&i))) {
+        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
+            continue;
         score = 0;
         if (fmt->name && short_name && av_match_name(short_name, fmt->name))
             score += 100;
-- 
2.46.0

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Re: [FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 1798 bytes --]

On Fri, Jun 06, 2025 at 12:06:34AM +0800, Zhao Zhili wrote:
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> ---
>  libavformat/avformat.h | 3 +--
>  libavformat/format.c   | 2 ++
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index 2034d2aecc..6edcf11022 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -470,8 +470,7 @@ typedef struct AVProbeData {
>  /**
>   * The muxer/demuxer is experimental and should be used with caution.
>   *
> - * - demuxers: will not be selected automatically by probing, must be specified
> - *             explicitly.
> + * Will not be selected automatically, must be specified explicitly.
>   */
>  #define AVFMT_EXPERIMENTAL  0x0004
>  #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
> diff --git a/libavformat/format.c b/libavformat/format.c
> index 71018ea6ab..516925e7e4 100644
> --- a/libavformat/format.c
> +++ b/libavformat/format.c
> @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
>      /* Find the proper file type. */
>      score_max = 0;
>      while ((fmt = av_muxer_iterate(&i))) {
> +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
> +            continue;

what does AVFMT_EXPERIMENTAL mean for a muxer ?

* a muxer could generate invalid, non compliant data
* a muxer could be insecure and exploitable
* a muxer could lack some feature (iam sure most muxers in most projects lack some feature)

I think the first 2 are reasons to use this flag

thx

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

There will always be a question for which you do not know the correct answer.

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Re: [FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[Kieran Kunhya via ffmpeg-devel]

On Fri, 6 Jun 2025, 10:51 Michael Niedermayer, <michael@niedermayer.cc>
wrote:

> On Fri, Jun 06, 2025 at 12:06:34AM +0800, Zhao Zhili wrote:
> > From: Zhao Zhili <zhilizhao@tencent.com>
> >
> > ---
> >  libavformat/avformat.h | 3 +--
> >  libavformat/format.c   | 2 ++
> >  2 files changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> > index 2034d2aecc..6edcf11022 100644
> > --- a/libavformat/avformat.h
> > +++ b/libavformat/avformat.h
> > @@ -470,8 +470,7 @@ typedef struct AVProbeData {
> >  /**
> >   * The muxer/demuxer is experimental and should be used with caution.
> >   *
> > - * - demuxers: will not be selected automatically by probing, must be
> specified
> > - *             explicitly.
> > + * Will not be selected automatically, must be specified explicitly.
> >   */
> >  #define AVFMT_EXPERIMENTAL  0x0004
> >  #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers.
> */
> > diff --git a/libavformat/format.c b/libavformat/format.c
> > index 71018ea6ab..516925e7e4 100644
> > --- a/libavformat/format.c
> > +++ b/libavformat/format.c
> > @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char
> *short_name, const char *filena
> >      /* Find the proper file type. */
> >      score_max = 0;
> >      while ((fmt = av_muxer_iterate(&i))) {
> > +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
> > +            continue;
>
> what does AVFMT_EXPERIMENTAL mean for a muxer ?
>
> * a muxer could generate invalid, non compliant data
> * a muxer could be insecure and exploitable
> * a muxer could lack some feature (iam sure most muxers in most projects
> lack some feature)
>
> I think the first 2 are reasons to use this flag
>

In the case of WebRTC it's 3. The user would expect it to work over the
internet (*Web*RTC after all) but it lacks NACK support so cannot recover
from any packet loss.

Without the experimental flag FFmpeg will get support tickets raised and
claims it is inferior to other implementations. Users will not be aware of
the lack of missing feature otherwise.

So it may be compliant on paper but it's not usable in the real world.

Kieran
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Re: [FFmpeg-devel] [PATCH] avformat/format: make experimental flag works for muxer

[Zhao Zhili]

> On Jun 6, 2025, at 18:00, Kieran Kunhya via ffmpeg-devel <ffmpeg-devel@ffmpeg.org> wrote:
> 
> On Fri, 6 Jun 2025, 10:51 Michael Niedermayer, <michael@niedermayer.cc>
> wrote:
> 
>> On Fri, Jun 06, 2025 at 12:06:34AM +0800, Zhao Zhili wrote:
>>> From: Zhao Zhili <zhilizhao@tencent.com>
>>> 
>>> ---
>>> libavformat/avformat.h | 3 +--
>>> libavformat/format.c   | 2 ++
>>> 2 files changed, 3 insertions(+), 2 deletions(-)
>>> 
>>> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
>>> index 2034d2aecc..6edcf11022 100644
>>> --- a/libavformat/avformat.h
>>> +++ b/libavformat/avformat.h
>>> @@ -470,8 +470,7 @@ typedef struct AVProbeData {
>>> /**
>>>  * The muxer/demuxer is experimental and should be used with caution.
>>>  *
>>> - * - demuxers: will not be selected automatically by probing, must be
>> specified
>>> - *             explicitly.
>>> + * Will not be selected automatically, must be specified explicitly.
>>>  */
>>> #define AVFMT_EXPERIMENTAL  0x0004
>>> #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers.
>> */
>>> diff --git a/libavformat/format.c b/libavformat/format.c
>>> index 71018ea6ab..516925e7e4 100644
>>> --- a/libavformat/format.c
>>> +++ b/libavformat/format.c
>>> @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char
>> *short_name, const char *filena
>>>     /* Find the proper file type. */
>>>     score_max = 0;
>>>     while ((fmt = av_muxer_iterate(&i))) {
>>> +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)
>>> +            continue;
>> 
>> what does AVFMT_EXPERIMENTAL mean for a muxer ?
>> 
>> * a muxer could generate invalid, non compliant data
>> * a muxer could be insecure and exploitable
>> * a muxer could lack some feature (iam sure most muxers in most projects
>> lack some feature)
>> 
>> I think the first 2 are reasons to use this flag
>> 
> 
> In the case of WebRTC it's 3. The user would expect it to work over the
> internet (*Web*RTC after all) but it lacks NACK support so cannot recover
> from any packet loss.
> 
> Without the experimental flag FFmpeg will get support tickets raised and
> claims it is inferior to other implementations. Users will not be aware of
> the lack of missing feature otherwise.
> 
> So it may be compliant on paper but it's not usable in the real world.

I have sent v2 to fix doc as suggested by James. Any comments on the
patch itself?

https://ffmpeg.org/pipermail/ffmpeg-devel/2025-June/344737.html

> 
> Kieran
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Re: [FFmpeg-devel] [PATCH v2] avformat/format: make experimental flag works for muxer

[Jack Lau]

> On Jun 6, 2025, at 12:44, Zhao Zhili <quinkblack-at-foxmail.com@ffmpeg.org> wrote:
> 
> From: Zhao Zhili <zhilizhao@tencent.com>
> 
> ---
> libavformat/avformat.h | 3 +--
> libavformat/format.c   | 2 ++
> 2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/avformat.h b/libavformat/avformat.h
> index 2034d2aecc..441e31bc2f 100644
> --- a/libavformat/avformat.h
> +++ b/libavformat/avformat.h
> @@ -470,8 +470,7 @@ typedef struct AVProbeData {
> /**
>  * The muxer/demuxer is experimental and should be used with caution.
>  *
> - * - demuxers: will not be selected automatically by probing, must be specified
> - *             explicitly.
> + * It will not be selected automatically, and must be specified explicitly.
>  */
> #define AVFMT_EXPERIMENTAL  0x0004
> #define AVFMT_SHOW_IDS      0x0008 /**< Show format stream IDs numbers. */
> diff --git a/libavformat/format.c b/libavformat/format.c
> index 71018ea6ab..516925e7e4 100644
> --- a/libavformat/format.c
> +++ b/libavformat/format.c
> @@ -95,6 +95,8 @@ const AVOutputFormat *av_guess_format(const char *short_name, const char *filena
>     /* Find the proper file type. */
>     score_max = 0;
>     while ((fmt = av_muxer_iterate(&i))) {
> +        if (fmt->flags & AVFMT_EXPERIMENTAL && !short_name)

If `&& !short_name` means this if check is always false as long as this muxer has a name?
Shouldn’t drop this `!` ?

> +            continue;
>         score = 0;
>         if (fmt->name && short_name && av_match_name(short_name, fmt->name))
>             score += 100;
> -- 
> 2.46.0
> 
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