[FFmpeg-devel] [PATCH 1/3] avcodec/ffv1enc: Slice combination is unsupported

[FFmpeg-devel] [PATCH 1/3] avcodec/ffv1enc: Slice combination is unsupported

[Michael Niedermayer]

We always write minimal slices, the size calculation is wrong in some
corner cases but as its always 1x1 (minus1) we can for now just hard-code it

This helps with ticket 5548

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1enc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavcodec/ffv1enc.c b/libavcodec/ffv1enc.c
index 2778c63012e..4d0ddc167ae 100644
--- a/libavcodec/ffv1enc.c
+++ b/libavcodec/ffv1enc.c
@@ -914,8 +914,8 @@ static void encode_slice_header(FFV1Context *f, FFV1Context *fs)
 
     put_symbol(c, state, (fs->slice_x     +1)*f->num_h_slices / f->width   , 0);
     put_symbol(c, state, (fs->slice_y     +1)*f->num_v_slices / f->height  , 0);
-    put_symbol(c, state, (fs->slice_width +1)*f->num_h_slices / f->width -1, 0);
-    put_symbol(c, state, (fs->slice_height+1)*f->num_v_slices / f->height-1, 0);
+    put_symbol(c, state, 0, 0);
+    put_symbol(c, state, 0, 0);
     for (j=0; j<f->plane_count; j++) {
         put_symbol(c, state, f->plane[j].quant_table_index, 0);
         av_assert0(f->plane[j].quant_table_index == f->context_model);
-- 
2.17.1

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[FFmpeg-devel] [PATCH 2/3] avcodec/ffv1: Store and reuse sx/sy

[Michael Niedermayer]

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1.c    | 2 ++
 libavcodec/ffv1.h    | 1 +
 libavcodec/ffv1enc.c | 4 ++--
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavcodec/ffv1.c b/libavcodec/ffv1.c
index b6204740edb..f44fead350b 100644
--- a/libavcodec/ffv1.c
+++ b/libavcodec/ffv1.c
@@ -129,6 +129,8 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
         fs->slice_height = sye - sys;
         fs->slice_x      = sxs;
         fs->slice_y      = sys;
+        fs->sx           = sx;
+        fs->sy           = sy;
 
         fs->sample_buffer = av_malloc_array((fs->width + 6), 3 * MAX_PLANES *
                                       sizeof(*fs->sample_buffer));
diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 04869da5c9a..14e40936065 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -129,6 +129,7 @@ typedef struct FFV1Context {
     int slice_height;
     int slice_x;
     int slice_y;
+    int sx, sy;
     int slice_reset_contexts;
     int slice_coding_mode;
     int slice_rct_by_coef;
diff --git a/libavcodec/ffv1enc.c b/libavcodec/ffv1enc.c
index 4d0ddc167ae..11be7fe32ea 100644
--- a/libavcodec/ffv1enc.c
+++ b/libavcodec/ffv1enc.c
@@ -912,8 +912,8 @@ static void encode_slice_header(FFV1Context *f, FFV1Context *fs)
     int j;
     memset(state, 128, sizeof(state));
 
-    put_symbol(c, state, (fs->slice_x     +1)*f->num_h_slices / f->width   , 0);
-    put_symbol(c, state, (fs->slice_y     +1)*f->num_v_slices / f->height  , 0);
+    put_symbol(c, state, fs->sx, 0);
+    put_symbol(c, state, fs->sy, 0);
     put_symbol(c, state, 0, 0);
     put_symbol(c, state, 0, 0);
     for (j=0; j<f->plane_count; j++) {
-- 
2.17.1

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[FFmpeg-devel] [PATCH 3/3] [RFC] avcodec/ffv1: Better rounding for slice positions

[Michael Niedermayer]

This fixes green lines in some odd dimensions with some slice configurations
like Ticket 5548

This also changes the encoder and whats encoded, and would require an
update to the specification. This change attempts to limit the change
to configurations that have missing lines currently.

Testing is welcome and needed

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/ffv1.c    | 38 ++++++++++++++++++++++++++++++++++----
 libavcodec/ffv1.h    |  2 ++
 libavcodec/ffv1dec.c |  8 ++++----
 libavcodec/ffv1enc.c |  7 ++++---
 4 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/libavcodec/ffv1.c b/libavcodec/ffv1.c
index f44fead350b..e780c910aee 100644
--- a/libavcodec/ffv1.c
+++ b/libavcodec/ffv1.c
@@ -103,6 +103,36 @@ av_cold int ff_ffv1_init_slices_state(FFV1Context *f)
     return 0;
 }
 
+int ff_need_new_slices(int width, int num_h_slices, int chroma_shift) {
+    int mpw = 1<<chroma_shift;
+    int i = width * (int64_t)(num_h_slices - 1) / num_h_slices;
+
+    return width % mpw && (width - i) % mpw == 0;
+}
+
+int ff_slice_coord(const FFV1Context *f, int width, int sx, int num_h_slices, int chroma_shift) {
+    int mpw = 1<<chroma_shift;
+    int awidth = FFALIGN(width, mpw);
+    int old = 1;
+
+    if (f->version > 4) {
+        old = 0;
+    } else if (f->version == 3 && f->micro_version > 4 ||
+               f->version == 4 && f->micro_version > 2
+    ) {
+        // If the old system will not encode all pixels we will choose the new
+        old = !ff_need_new_slices(width, num_h_slices, chroma_shift);
+    }
+
+    if (old)
+        return width * sx / num_h_slices;
+
+    sx = (awidth * (int64_t)sx + (num_h_slices * mpw / 2)) / (num_h_slices * mpw) * mpw;
+    if (sx == awidth)
+        sx = width;
+    return sx;
+}
+
 av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
 {
     int i, max_slice_count = f->num_h_slices * f->num_v_slices;
@@ -112,10 +142,10 @@ av_cold int ff_ffv1_init_slice_contexts(FFV1Context *f)
     for (i = 0; i < max_slice_count;) {
         int sx          = i % f->num_h_slices;
         int sy          = i / f->num_h_slices;
-        int sxs         = f->avctx->width  *  sx      / f->num_h_slices;
-        int sxe         = f->avctx->width  * (sx + 1) / f->num_h_slices;
-        int sys         = f->avctx->height *  sy      / f->num_v_slices;
-        int sye         = f->avctx->height * (sy + 1) / f->num_v_slices;
+        int sxs         = ff_slice_coord(f, f->avctx->width , sx    , f->num_h_slices, f->chroma_h_shift);
+        int sxe         = ff_slice_coord(f, f->avctx->width , sx + 1, f->num_h_slices, f->chroma_h_shift);
+        int sys         = ff_slice_coord(f, f->avctx->height, sy   ,  f->num_v_slices, f->chroma_v_shift);
+        int sye         = ff_slice_coord(f, f->avctx->height, sy + 1, f->num_v_slices, f->chroma_v_shift);
         FFV1Context *fs = av_mallocz(sizeof(*fs));
 
         if (!fs)
diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
index 14e40936065..3f658a26522 100644
--- a/libavcodec/ffv1.h
+++ b/libavcodec/ffv1.h
@@ -143,6 +143,8 @@ int ff_ffv1_init_slice_contexts(FFV1Context *f);
 int ff_ffv1_allocate_initial_states(FFV1Context *f);
 void ff_ffv1_clear_slice_state(const FFV1Context *f, FFV1Context *fs);
 int ff_ffv1_close(AVCodecContext *avctx);
+int ff_need_new_slices(int width, int num_h_slices, int chroma_shift);
+int ff_slice_coord(const FFV1Context *f, int width, int sx, int num_h_slices, int chroma_shift);
 
 static av_always_inline int fold(int diff, int bits)
 {
diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
index a376a4c8170..0486938eb2b 100644
--- a/libavcodec/ffv1dec.c
+++ b/libavcodec/ffv1dec.c
@@ -184,10 +184,10 @@ static int decode_slice_header(const FFV1Context *f, FFV1Context *fs)
     if (sx > f->num_h_slices - sw || sy > f->num_v_slices - sh)
         return AVERROR_INVALIDDATA;
 
-    fs->slice_x      =  sx       * (int64_t)f->width  / f->num_h_slices;
-    fs->slice_y      =  sy       * (int64_t)f->height / f->num_v_slices;
-    fs->slice_width  = (sx + sw) * (int64_t)f->width  / f->num_h_slices - fs->slice_x;
-    fs->slice_height = (sy + sh) * (int64_t)f->height / f->num_v_slices - fs->slice_y;
+    fs->slice_x      =  ff_slice_coord(f, f->width , sx     , f->num_h_slices, f->chroma_h_shift);
+    fs->slice_y      =  ff_slice_coord(f, f->height, sy     , f->num_v_slices, f->chroma_v_shift);
+    fs->slice_width  =  ff_slice_coord(f, f->width , sx + sw, f->num_h_slices, f->chroma_h_shift) - fs->slice_x;
+    fs->slice_height =  ff_slice_coord(f, f->height, sy + sh, f->num_v_slices, f->chroma_v_shift) - fs->slice_y;
 
     av_assert0((unsigned)fs->slice_width  <= f->width &&
                 (unsigned)fs->slice_height <= f->height);
diff --git a/libavcodec/ffv1enc.c b/libavcodec/ffv1enc.c
index 11be7fe32ea..e04695efa93 100644
--- a/libavcodec/ffv1enc.c
+++ b/libavcodec/ffv1enc.c
@@ -397,7 +397,8 @@ static int write_extradata(FFV1Context *f)
     int i, j, k;
     uint8_t state2[32][CONTEXT_SIZE];
     unsigned v;
-
+    int need_new_slices = ff_need_new_slices(f->avctx->width , f->num_h_slices, f->chroma_h_shift)
+                        ||ff_need_new_slices(f->avctx->height, f->num_v_slices, f->chroma_v_shift);
     memset(state2, 128, sizeof(state2));
     memset(state, 128, sizeof(state));
 
@@ -412,9 +413,9 @@ static int write_extradata(FFV1Context *f)
     put_symbol(c, state, f->version, 0);
     if (f->version > 2) {
         if (f->version == 3) {
-            f->micro_version = 4;
+            f->micro_version = 4 + need_new_slices;
         } else if (f->version == 4)
-            f->micro_version = 2;
+            f->micro_version = 2 + need_new_slices;
         put_symbol(c, state, f->micro_version, 0);
     }
 
-- 
2.17.1

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Re: [FFmpeg-devel] [PATCH 3/3] [RFC] avcodec/ffv1: Better rounding for slice positions

[Jerome Martinez]

On 07/10/2023 02:14, Michael Niedermayer wrote:
> This fixes green lines in some odd dimensions with some slice configurations
> like Ticket 5548
>
> This also changes the encoder and whats encoded, and would require an
> update to the specification. This change attempts to limit the change
> to configurations that have missing lines currently.

It changes a lot the count of pixels per slice, and , e.g. with 4:2:2 and 4 slices per direction (16 slices in total), 13 pixel width:
before: 3/3/3/4 for luma, 2/2/2/2 for chroma (so 1 chroma too much)
after: 4/4/2/3 for luma, 2/2/1/2 for chroma

Wouldn't it easier for spec and maths to keep the previous behavior for luma and consider extra chroma as to be not encoded?
Something like 3/3/3/4 for luma, 2/2/2/1 for chroma
Actually maybe not really a change for spec in that case, more making a part more explicit while considering the patch as a bug fix rather than a spec change.

Or did I miss another issue? I'll check more a bit later.

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Re: [FFmpeg-devel] [PATCH 3/3] [RFC] avcodec/ffv1: Better rounding for slice positions

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 2323 bytes --]

On Sat, Oct 07, 2023 at 06:52:07AM +0200, Jerome Martinez wrote:
> On 07/10/2023 02:14, Michael Niedermayer wrote:
> > This fixes green lines in some odd dimensions with some slice configurations
> > like Ticket 5548
> > 
> > This also changes the encoder and whats encoded, and would require an
> > update to the specification. This change attempts to limit the change
> > to configurations that have missing lines currently.
> 
> It changes a lot the count of pixels per slice, and , e.g. with 4:2:2 and 4 slices per direction (16 slices in total), 13 pixel width:
> before: 3/3/3/4 for luma, 2/2/2/2 for chroma (so 1 chroma too much)
> after: 4/4/2/3 for luma, 2/2/1/2 for chroma
> 
> Wouldn't it easier for spec and maths to keep the previous behavior for luma and consider extra chroma as to be not encoded?
> Something like 3/3/3/4 for luma, 2/2/2/1 for chroma
> Actually maybe not really a change for spec in that case, more making a part more explicit while considering the patch as a bug fix rather than a spec change.
> 

> Or did I miss another issue? I'll check more a bit later.

The existing thing has a few odd behaviors in corner cases
1. sometimes its not encoding the rightmost & bottommost chroma (leaving a green line)
2. sometimes its encoding chroma columns/rows in more than one slice (which is a waste of bits)

iam not sure if the chrome that gets encoded in each slice is entirely
expected, i guess it depends on what one expects

The new code tries to keep slices size a multiple of the chroma subsampling
factor. That way the left top coordinate of every 4:2:0 slice would always be
even for example and only the last ones could have right / bottom odd when  the
whole image has odd width/height

But this is a RFC for exactly the reasons that you mention, it changes things
and would become the default in future versions

Any future compression between luma and chroma planes may benefit from slices
being less odd in their chroma vs luma coordinates. But noone is working on
this AFAIK. Its just hypothetical

thx

[...]

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Some people wanted to paint the bikeshed green, some blue and some pink.
People argued and fought, when they finally agreed, only rust was left.

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