ffmpeg h264_metadata_bsf issue

gistfile1.txt

$ wget https://tmm1.s3.amazonaws.com/h264-metadata.mpg

$ ffmpeg -i h264-metadata.mpg -c copy -map v -f h264 -y /dev/stdout | h264_analyze /dev/stdin > /tmp/a.out
$ ffmpeg -i h264-metadata.mpg -bsf:v h264_metadata -c copy -map v -f h264 -y /dev/stdout | h264_analyze /dev/stdin > /tmp/b.out

$ diff -uNdr /tmp/a.out /tmp/b.out | head -20
--- /tmp/a.out     2019-10-09 14:33:07.000000000 -0700
+++ /tmp/b.out  2019-10-09 14:33:01.000000000 -0700
@@ -144,8 +144,8 @@
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 00 00 00 00
-!! Found NAL at offset 150 (0x0096), size 245633 (0x3BF81)
-XX 00 00 00 01 41 88 8E 09 68 62 C2 32 89 A8 BB 23
+!! Found NAL at offset 149 (0x0095), size 245633 (0x3BF81)
+XX 80 00 00 01 41 88 8E 09 68 62 C2 32 89 A8 BB 23

 ==================== NAL ====================
  forbidden_zero_bit : 0
@@ -184,7 +184,7 @@
  no_output_of_prior_pics_flag : 0
  long_term_reference_flag : 0
  adaptive_ref_pic_marking_mode_flag : 1
-!! Found NAL at offset 245792 (0x3C020), size 2 (0x0002)
+!! Found NAL at offset 245786 (0x3C01A), size 2 (0x0002)
 XX 00 00 00 01 09 50

h264bsf.patch

diff --git a/libavcodec/cbs_h2645.c b/libavcodec/cbs_h2645.c
index d39173b408..1f5c4f0525 100644
--- a/libavcodec/cbs_h2645.c
+++ b/libavcodec/cbs_h2645.c
@@ -565,9 +565,11 @@ static int cbs_h2645_fragment_add_nals(CodedBitstreamContext *ctx,
         AVBufferRef *ref;
         size_t size = nal->size;

+        if (nal->type != H264_NAL_SLICE && nal->type != H264_NAL_IDR_SLICE) {
         // Remove trailing zeroes.
         while (size > 0 && nal->data[size - 1] == 0)
             --size;
+        }
         if (size == 0)
             continue;

@@ -858,13 +860,13 @@ static int cbs_h264_read_nal_unit(CodedBitstreamContext *ctx,

             pos = get_bits_count(&gbc);
             len = unit->data_size;
-            if (!unit->data[len - 1]) {
+            /*if (!unit->data[len - 1]) {
                 int z;
                 for (z = 0; z < len && !unit->data[len - z - 1]; z++);
                 av_log(ctx->log_ctx, AV_LOG_DEBUG, "Deleted %d trailing zeroes "
                        "from slice data.\n", z);
                 len -= z;
-            }
+            }*/

             slice->data_size = len - pos / 8;
             slice->data_ref  = av_buffer_ref(unit->data_ref);
@@ -1465,6 +1467,7 @@ static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
     dp = 0;
     for (i = 0; i < frag->nb_units; i++) {
         CodedBitstreamUnit *unit = &frag->units[i];
+        size_t size;

         if (unit->data_bit_padding > 0) {
             if (i < frag->nb_units - 1)
@@ -1491,7 +1494,10 @@ static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
         data[dp++] = 1;

         zero_run = 0;
-        for (sp = 0; sp < unit->data_size; sp++) {
+        size = unit->data_size;
+        while (size > 0 && unit->data[size - 1] == 0)
+            --size;
+        for (sp = 0; sp < size; sp++) {
             if (zero_run < 2) {
                 if (unit->data[sp] == 0)
                     ++zero_run;
@@ -1506,6 +1512,9 @@ static int cbs_h2645_assemble_fragment(CodedBitstreamContext *ctx,
             }
             data[dp++] = unit->data[sp];
         }
+        size = unit->data_size - size;
+        for (sp = 0; sp < size; sp++)
+            data[dp++] = 0;
     }

     av_assert0(dp <= max_size);

summary.md

on an android device with MTK8695+MT7668, using avcodec/mediacodec with OMX.MTK.VIDEO.DECODER.AVC

observed that using either chomp_bsf or h264_metadata_bsf makes the sample stall out the hardware decoder due to trailing zeros being removed from the end of NAL_SLICE and NAL_IDR_SLICE

with the patch above, cbs keeps trailing zeros and fixes playback on the device when using h264_metadata_bsf (and possibly also when using filter_units_bsf).