[FFmpeg-devel] [PATCH 1/3] avcodec/h264_slice: Fix decoding undamaged input with slices

[FFmpeg-devel] [PATCH 1/3] avcodec/h264_slice: Fix decoding undamaged input with slices

[Andreas Rheinhardt]

ff_er_frame_start() initializes ERContext.error_count
to three times the number of macroblocks to decode.
Later ff_er_add_slice() reduces this number by the amount
of macroblocks whose AC resp. DC resp. MV have been finished
(so every correctly decoded MB counts three times).
So the frame has been decoded correctly if error_count is zero
at the end.

The H.264 decoder uses multiple ERContexts when using
slice threading and therefore combines these error counts:
The first slice's ERContext is intended to be initialized
by ff_er_frame_start(), error_count of all the other
slice contexts is intended to be zeroed initially and
all afterwards all the error_counts are summed.

Yet commit 43b434210e597d484aef57c4139c3126d22b7e2b
(probably unintentionally) changed the code to set
the first slice's error_count to zero as well.
This leads to bogus error messages in case one decodes
an input video using multiple slices with slice threading
with error concealment enabled (which is not the default)
("concealing 0 DC, 0 AC, 0 MV errors in [IPB] frame");
furthermore the returned frame is marked as corrupt as well
(ffmpeg reports "corrupt decoded frame in stream %d" for this).

This can be fixed easily given that only the first ERContext
is really used since 7be2d2a70cd20d88fd826a83f87037d14681a579:
Don't reset the error_count; and don't sum the error counts as well.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/h264_slice.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index ee84b3764d..f6104dde89 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -2931,9 +2931,6 @@ int ff_h264_execute_decode_slices(H264Context *h)
             int slice_idx;
 
             sl                 = &h->slice_ctx[i];
-            if (CONFIG_ERROR_RESILIENCE) {
-                sl->er.error_count = 0;
-            }
 
             /* make sure none of those slices overlap */
             slice_idx = sl->mb_y * h->mb_width + sl->mb_x;
@@ -2954,10 +2951,6 @@ int ff_h264_execute_decode_slices(H264Context *h)
         /* pull back stuff from slices to master context */
         sl                   = &h->slice_ctx[context_count - 1];
         h->mb_y              = sl->mb_y;
-        if (CONFIG_ERROR_RESILIENCE) {
-            for (i = 1; i < context_count; i++)
-                h->slice_ctx[0].er.error_count += h->slice_ctx[i].er.error_count;
-        }
 
         if (h->postpone_filter) {
             h->postpone_filter = 0;
-- 
2.32.0

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[FFmpeg-devel] [PATCH 2/3] avcodec/h264dec: Move ERContext to H264Context

[Andreas Rheinhardt]

Since 7be2d2a70cd20d88fd826a83f87037d14681a579 only one context
is used. Moving it to H264Context from H264SliceContext is natural.

One could access the ERContext from H264SliceContext
via H264SliceContext.h264->er; yet H264SliceContext.h264 should
naturally be const-qualified, because slice threads should not
modify the main context. The ERContext is an exception
to this, as ff_er_add_slice() is intended to be called simultaneously
by multiple threads. And for this one needs a pointer whose
pointed-to-type is not const-qualified.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/h264_slice.c | 31 ++++++---------
 libavcodec/h264dec.c    | 86 ++++++++++++++++++++---------------------
 libavcodec/h264dec.h    |  7 ++--
 3 files changed, 56 insertions(+), 68 deletions(-)

diff --git a/libavcodec/h264_slice.c b/libavcodec/h264_slice.c
index f6104dde89..d56722a5c2 100644
--- a/libavcodec/h264_slice.c
+++ b/libavcodec/h264_slice.c
@@ -537,7 +537,7 @@ static int h264_frame_start(H264Context *h)
     h->cur_pic_ptr = pic;
     ff_h264_unref_picture(h, &h->cur_pic);
     if (CONFIG_ERROR_RESILIENCE) {
-        ff_h264_set_erpic(&h->slice_ctx[0].er.cur_pic, NULL);
+        ff_h264_set_erpic(&h->er.cur_pic, NULL);
     }
 
     if ((ret = ff_h264_ref_picture(h, &h->cur_pic, h->cur_pic_ptr)) < 0)
@@ -549,9 +549,9 @@ static int h264_frame_start(H264Context *h)
     }
 
     if (CONFIG_ERROR_RESILIENCE && h->enable_er) {
-        ff_er_frame_start(&h->slice_ctx[0].er);
-        ff_h264_set_erpic(&h->slice_ctx[0].er.last_pic, NULL);
-        ff_h264_set_erpic(&h->slice_ctx[0].er.next_pic, NULL);
+        ff_er_frame_start(&h->er);
+        ff_h264_set_erpic(&h->er.last_pic, NULL);
+        ff_h264_set_erpic(&h->er.next_pic, NULL);
     }
 
     for (i = 0; i < 16; i++) {
@@ -1004,11 +1004,7 @@ static int h264_slice_header_init(H264Context *h)
     ff_videodsp_init(&h->vdsp, sps->bit_depth_luma);
 
     if (!HAVE_THREADS || !(h->avctx->active_thread_type & FF_THREAD_SLICE)) {
-        ret = ff_h264_slice_context_init(h, &h->slice_ctx[0]);
-        if (ret < 0) {
-            av_log(h->avctx, AV_LOG_ERROR, "context_init() failed.\n");
-            goto fail;
-        }
+        ff_h264_slice_context_init(h, &h->slice_ctx[0]);
     } else {
         for (i = 0; i < h->nb_slice_ctx; i++) {
             H264SliceContext *sl = &h->slice_ctx[i];
@@ -1018,10 +1014,7 @@ static int h264_slice_header_init(H264Context *h)
             sl->mvd_table[0]       = h->mvd_table[0]       + i * 8 * 2 * h->mb_stride;
             sl->mvd_table[1]       = h->mvd_table[1]       + i * 8 * 2 * h->mb_stride;
 
-            if ((ret = ff_h264_slice_context_init(h, sl)) < 0) {
-                av_log(h->avctx, AV_LOG_ERROR, "context_init() failed.\n");
-                goto fail;
-            }
+            ff_h264_slice_context_init(h, sl);
         }
     }
 
@@ -2667,7 +2660,7 @@ static void decode_finish_row(const H264Context *h, H264SliceContext *sl)
 
     ff_h264_draw_horiz_band(h, sl, top, height);
 
-    if (h->droppable || sl->h264->slice_ctx[0].er.error_occurred)
+    if (h->droppable || h->er.error_occurred)
         return;
 
     ff_thread_report_progress(&h->cur_pic_ptr->tf, top + height - 1,
@@ -2682,9 +2675,7 @@ static void er_add_slice(H264SliceContext *sl,
         return;
 
     if (CONFIG_ERROR_RESILIENCE) {
-        ERContext *er = &sl->h264->slice_ctx[0].er;
-
-        ff_er_add_slice(er, startx, starty, endx, endy, status);
+        ff_er_add_slice(sl->er, startx, starty, endx, endy, status);
     }
 }
 
@@ -2713,13 +2704,13 @@ static int decode_slice(struct AVCodecContext *avctx, void *arg)
     sl->is_complex = FRAME_MBAFF(h) || h->picture_structure != PICT_FRAME ||
                      (CONFIG_GRAY && (h->flags & AV_CODEC_FLAG_GRAY));
 
-    if (!(h->avctx->active_thread_type & FF_THREAD_SLICE) && h->picture_structure == PICT_FRAME && h->slice_ctx[0].er.error_status_table) {
+    if (!(h->avctx->active_thread_type & FF_THREAD_SLICE) && h->picture_structure == PICT_FRAME && sl->er->error_status_table) {
         const int start_i  = av_clip(sl->resync_mb_x + sl->resync_mb_y * h->mb_width, 0, h->mb_num - 1);
         if (start_i) {
-            int prev_status = h->slice_ctx[0].er.error_status_table[h->slice_ctx[0].er.mb_index2xy[start_i - 1]];
+            int prev_status = sl->er->error_status_table[sl->er->mb_index2xy[start_i - 1]];
             prev_status &= ~ VP_START;
             if (prev_status != (ER_MV_END | ER_DC_END | ER_AC_END))
-                h->slice_ctx[0].er.error_occurred = 1;
+                sl->er->error_occurred = 1;
         }
     }
 
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index 2a510b0a01..f438376431 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -154,14 +154,16 @@ void ff_h264_free_tables(H264Context *h)
     av_buffer_pool_uninit(&h->motion_val_pool);
     av_buffer_pool_uninit(&h->ref_index_pool);
 
+#if CONFIG_ERROR_RESILIENCE
+    av_freep(&h->er.mb_index2xy);
+    av_freep(&h->er.error_status_table);
+    av_freep(&h->er.er_temp_buffer);
+    av_freep(&h->dc_val_base);
+#endif
+
     for (i = 0; i < h->nb_slice_ctx; i++) {
         H264SliceContext *sl = &h->slice_ctx[i];
 
-        av_freep(&sl->dc_val_base);
-        av_freep(&sl->er.mb_index2xy);
-        av_freep(&sl->er.error_status_table);
-        av_freep(&sl->er.er_temp_buffer);
-
         av_freep(&sl->bipred_scratchpad);
         av_freep(&sl->edge_emu_buffer);
         av_freep(&sl->top_borders[0]);
@@ -176,6 +178,7 @@ void ff_h264_free_tables(H264Context *h)
 
 int ff_h264_alloc_tables(H264Context *h)
 {
+    ERContext *const er = &h->er;
     const int big_mb_num = h->mb_stride * (h->mb_height + 1);
     const int row_mb_num = 2*h->mb_stride*FFMAX(h->nb_slice_ctx, 1);
     const int st_size = big_mb_num + h->mb_stride;
@@ -208,33 +211,11 @@ int ff_h264_alloc_tables(H264Context *h)
             h->mb2br_xy[mb_xy] = 8 * (FMO ? mb_xy : (mb_xy % (2 * h->mb_stride)));
         }
 
-    return 0;
-}
-
-/**
- * Init context
- * Allocate buffers which are not shared amongst multiple threads.
- */
-int ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl)
-{
-    ERContext *er = &sl->er;
-    int mb_array_size = h->mb_height * h->mb_stride;
-    int y_size  = (2 * h->mb_width + 1) * (2 * h->mb_height + 1);
-    int c_size  = h->mb_stride * (h->mb_height + 1);
-    int yc_size = y_size + 2   * c_size;
-    int x, y, i;
-
-    sl->ref_cache[0][scan8[5]  + 1] =
-    sl->ref_cache[0][scan8[7]  + 1] =
-    sl->ref_cache[0][scan8[13] + 1] =
-    sl->ref_cache[1][scan8[5]  + 1] =
-    sl->ref_cache[1][scan8[7]  + 1] =
-    sl->ref_cache[1][scan8[13] + 1] = PART_NOT_AVAILABLE;
-
-    if (sl != h->slice_ctx) {
-        memset(er, 0, sizeof(*er));
-    } else if (CONFIG_ERROR_RESILIENCE) {
+    if (CONFIG_ERROR_RESILIENCE) {
         const int er_size = h->mb_height * h->mb_stride * (4*sizeof(int) + 1);
+        int mb_array_size = h->mb_height * h->mb_stride;
+        int y_size  = (2 * h->mb_width + 1) * (2 * h->mb_height + 1);
+        int yc_size = y_size + 2 * big_mb_num;
 
         /* init ER */
         er->avctx          = h->avctx;
@@ -252,7 +233,7 @@ int ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl)
         if (!FF_ALLOCZ_TYPED_ARRAY(er->mb_index2xy,        h->mb_num + 1) ||
             !FF_ALLOCZ_TYPED_ARRAY(er->error_status_table, mb_array_size) ||
             !FF_ALLOCZ_TYPED_ARRAY(er->er_temp_buffer,     er_size)       ||
-            !FF_ALLOCZ_TYPED_ARRAY(sl->dc_val_base,        yc_size))
+            !FF_ALLOCZ_TYPED_ARRAY(h->dc_val_base,         yc_size))
             return AVERROR(ENOMEM); // ff_h264_free_tables will clean up for us
 
         for (y = 0; y < h->mb_height; y++)
@@ -261,16 +242,31 @@ int ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl)
 
         er->mb_index2xy[h->mb_height * h->mb_width] = (h->mb_height - 1) *
                                                       h->mb_stride + h->mb_width;
-        er->dc_val[0] = sl->dc_val_base + h->mb_width * 2 + 2;
-        er->dc_val[1] = sl->dc_val_base + y_size + h->mb_stride + 1;
-        er->dc_val[2] = er->dc_val[1] + c_size;
-        for (i = 0; i < yc_size; i++)
-            sl->dc_val_base[i] = 1024;
+        er->dc_val[0] = h->dc_val_base + h->mb_width * 2 + 2;
+        er->dc_val[1] = h->dc_val_base + y_size + h->mb_stride + 1;
+        er->dc_val[2] = er->dc_val[1] + big_mb_num;
+        for (int i = 0; i < yc_size; i++)
+            h->dc_val_base[i] = 1024;
     }
 
     return 0;
 }
 
+/**
+ * Init slice context
+ */
+void ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl)
+{
+    sl->ref_cache[0][scan8[5]  + 1] =
+    sl->ref_cache[0][scan8[7]  + 1] =
+    sl->ref_cache[0][scan8[13] + 1] =
+    sl->ref_cache[1][scan8[5]  + 1] =
+    sl->ref_cache[1][scan8[7]  + 1] =
+    sl->ref_cache[1][scan8[13] + 1] = PART_NOT_AVAILABLE;
+
+    sl->er = &h->er;
+}
+
 static int h264_init_pic(H264Picture *pic)
 {
     pic->f = av_frame_alloc();
@@ -739,7 +735,7 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
         goto end;
 
     // set decode_error_flags to allow users to detect concealed decoding errors
-    if ((ret < 0 || h->slice_ctx->er.error_occurred) && h->cur_pic_ptr) {
+    if ((ret < 0 || h->er.error_occurred) && h->cur_pic_ptr) {
         h->cur_pic_ptr->f->decode_error_flags |= FF_DECODE_ERROR_DECODE_SLICES;
     }
 
@@ -764,25 +760,25 @@ end:
         H264SliceContext *sl = h->slice_ctx;
         int use_last_pic = h->last_pic_for_ec.f->buf[0] && !sl->ref_count[0];
 
-        ff_h264_set_erpic(&sl->er.cur_pic, h->cur_pic_ptr);
+        ff_h264_set_erpic(&h->er.cur_pic, h->cur_pic_ptr);
 
         if (use_last_pic) {
-            ff_h264_set_erpic(&sl->er.last_pic, &h->last_pic_for_ec);
+            ff_h264_set_erpic(&h->er.last_pic, &h->last_pic_for_ec);
             sl->ref_list[0][0].parent = &h->last_pic_for_ec;
             memcpy(sl->ref_list[0][0].data, h->last_pic_for_ec.f->data, sizeof(sl->ref_list[0][0].data));
             memcpy(sl->ref_list[0][0].linesize, h->last_pic_for_ec.f->linesize, sizeof(sl->ref_list[0][0].linesize));
             sl->ref_list[0][0].reference = h->last_pic_for_ec.reference;
         } else if (sl->ref_count[0]) {
-            ff_h264_set_erpic(&sl->er.last_pic, sl->ref_list[0][0].parent);
+            ff_h264_set_erpic(&h->er.last_pic, sl->ref_list[0][0].parent);
         } else
-            ff_h264_set_erpic(&sl->er.last_pic, NULL);
+            ff_h264_set_erpic(&h->er.last_pic, NULL);
 
         if (sl->ref_count[1])
-            ff_h264_set_erpic(&sl->er.next_pic, sl->ref_list[1][0].parent);
+            ff_h264_set_erpic(&h->er.next_pic, sl->ref_list[1][0].parent);
 
-        sl->er.ref_count = sl->ref_count[0];
+        h->er.ref_count = sl->ref_count[0];
 
-        ff_er_frame_end(&sl->er);
+        ff_er_frame_end(&h->er);
         if (use_last_pic)
             memset(&sl->ref_list[0][0], 0, sizeof(sl->ref_list[0][0]));
     }
diff --git a/libavcodec/h264dec.h b/libavcodec/h264dec.h
index 6ad2333419..0b9c5784a2 100644
--- a/libavcodec/h264dec.h
+++ b/libavcodec/h264dec.h
@@ -170,7 +170,7 @@ typedef struct H264Ref {
 typedef struct H264SliceContext {
     struct H264Context *h264;
     GetBitContext gb;
-    ERContext er;
+    ERContext *er;
 
     int slice_num;
     int slice_type;
@@ -271,7 +271,6 @@ typedef struct H264SliceContext {
     unsigned int pps_id;
 
     const uint8_t *intra_pcm_ptr;
-    int16_t *dc_val_base;
 
     uint8_t *bipred_scratchpad;
     uint8_t *edge_emu_buffer;
@@ -543,6 +542,8 @@ typedef struct H264Context {
     int height_from_caller;
 
     int enable_er;
+    ERContext er;
+    int16_t *dc_val_base;
 
     H264SEIContext sei;
 
@@ -784,7 +785,7 @@ int ff_h264_ref_picture(H264Context *h, H264Picture *dst, H264Picture *src);
 int ff_h264_replace_picture(H264Context *h, H264Picture *dst, const H264Picture *src);
 void ff_h264_unref_picture(H264Context *h, H264Picture *pic);
 
-int ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl);
+void ff_h264_slice_context_init(H264Context *h, H264SliceContext *sl);
 
 void ff_h264_draw_horiz_band(const H264Context *h, H264SliceContext *sl, int y, int height);
 
-- 
2.32.0

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[FFmpeg-devel] [PATCH 3/3] avcodec/h264dec: Constify slices' pointer to the parent context

[Andreas Rheinhardt]

Modifying the main context by a slice thread is racy;
so constify the pointer to it in H264SliceContext.
The code itself was already compatible with this change.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/h264dec.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/h264dec.h b/libavcodec/h264dec.h
index 0b9c5784a2..9a1ec1bace 100644
--- a/libavcodec/h264dec.h
+++ b/libavcodec/h264dec.h
@@ -168,7 +168,7 @@ typedef struct H264Ref {
 } H264Ref;
 
 typedef struct H264SliceContext {
-    struct H264Context *h264;
+    const struct H264Context *h264;
     GetBitContext gb;
     ERContext *er;
 
-- 
2.32.0

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[FFmpeg-devel] [PATCH 4/4] avcodec/error_resilience: Remove write only ERContext.ref_count

[Andreas Rheinhardt]

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 libavcodec/error_resilience.h | 1 -
 libavcodec/h264dec.c          | 2 --
 2 files changed, 3 deletions(-)

diff --git a/libavcodec/error_resilience.h b/libavcodec/error_resilience.h
index bb770ff674..2187586618 100644
--- a/libavcodec/error_resilience.h
+++ b/libavcodec/error_resilience.h
@@ -81,7 +81,6 @@ typedef struct ERContext {
     uint16_t pb_time;
     int quarter_sample;
     int partitioned_frame;
-    int ref_count;
 
     void (*decode_mb)(void *opaque, int ref, int mv_dir, int mv_type,
                       int (*mv)[2][4][2],
diff --git a/libavcodec/h264dec.c b/libavcodec/h264dec.c
index f438376431..9faa35e36d 100644
--- a/libavcodec/h264dec.c
+++ b/libavcodec/h264dec.c
@@ -776,8 +776,6 @@ end:
         if (sl->ref_count[1])
             ff_h264_set_erpic(&h->er.next_pic, sl->ref_list[1][0].parent);
 
-        h->er.ref_count = sl->ref_count[0];
-
         ff_er_frame_end(&h->er);
         if (use_last_pic)
             memset(&sl->ref_list[0][0], 0, sizeof(sl->ref_list[0][0]));
-- 
2.32.0

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Re: [FFmpeg-devel] [PATCH 1/3] avcodec/h264_slice: Fix decoding undamaged input with slices

[Michael Niedermayer]

[-- Attachment #1.1: Type: text/plain, Size: 2091 bytes --]

On Thu, Mar 24, 2022 at 09:20:06PM +0100, Andreas Rheinhardt wrote:
> ff_er_frame_start() initializes ERContext.error_count
> to three times the number of macroblocks to decode.
> Later ff_er_add_slice() reduces this number by the amount
> of macroblocks whose AC resp. DC resp. MV have been finished
> (so every correctly decoded MB counts three times).
> So the frame has been decoded correctly if error_count is zero
> at the end.
> 
> The H.264 decoder uses multiple ERContexts when using
> slice threading and therefore combines these error counts:
> The first slice's ERContext is intended to be initialized
> by ff_er_frame_start(), error_count of all the other
> slice contexts is intended to be zeroed initially and
> all afterwards all the error_counts are summed.
> 
> Yet commit 43b434210e597d484aef57c4139c3126d22b7e2b
> (probably unintentionally) changed the code to set
> the first slice's error_count to zero as well.
> This leads to bogus error messages in case one decodes
> an input video using multiple slices with slice threading
> with error concealment enabled (which is not the default)
> ("concealing 0 DC, 0 AC, 0 MV errors in [IPB] frame");
> furthermore the returned frame is marked as corrupt as well
> (ffmpeg reports "corrupt decoded frame in stream %d" for this).
> 
> This can be fixed easily given that only the first ERContext
> is really used since 7be2d2a70cd20d88fd826a83f87037d14681a579:
> Don't reset the error_count; and don't sum the error counts as well.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/h264_slice.c | 7 -------
>  1 file changed, 7 deletions(-)

this patchset is a nice cleanup/fix to the error concealment code
in h264

thx

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

Frequently ignored answer#1 FFmpeg bugs should be sent to our bugtracker. User
questions about the command line tools should be sent to the ffmpeg-user ML.
And questions about how to use libav* should be sent to the libav-user ML.

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