[FFmpeg-devel] [PATCH] avcodec/cbs_av1: don't abort when splitting Temporal Units containing OBUs with no obu_size field

[Mark Thompson]

On 15/11/18 04:27, James Almer wrote:
> The ISOBMFF and Matroska specs allow the last OBU in a Sample/Block to have
> obu_has_size_field equal to 0.
> 
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
> See https://0x0.st/sUsU.mp4
> 
> It apparently can't be decoded with either aom or dav1d atm, but the latter
> should be able to soon.
> You can try remuxing it using the av1_metadata bsf after this patch while at it,
> since the code to write obu_size fields unconditionally is still in place, and
> that should make it decodable with either library.

I wonder whether there should be an option somewhere for omitting the last size field when writing?  It would save a few bytes on every TU when using any container which already has sizes.

> For some reason cbs_av1_read_unit() is already able to handle OBUs with no
> obu_size field. It was only cbs_av1_split_fragment() bailing out with them.

That came from the annex B support, before we decided that AVPackets would never contain annex B.

>  libavcodec/cbs_av1.c | 16 ++++++----------
>  1 file changed, 6 insertions(+), 10 deletions(-)
> 
> diff --git a/libavcodec/cbs_av1.c b/libavcodec/cbs_av1.c
> index ed5211be19..e02bc7027a 100644
> --- a/libavcodec/cbs_av1.c
> +++ b/libavcodec/cbs_av1.c
> @@ -788,13 +788,6 @@ static int cbs_av1_split_fragment(CodedBitstreamContext *ctx,
>          if (err < 0)
>              goto fail;
>  
> -        if (!header.obu_has_size_field) {
> -            av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid OBU for raw "
> -                   "stream: size field must be present.\n");
> -            err = AVERROR_INVALIDDATA;
> -            goto fail;
> -        }
> -
>          if (get_bits_left(&gbc) < 8) {
>              av_log(ctx->log_ctx, AV_LOG_ERROR, "Invalid OBU: fragment "
>                     "too short (%zu bytes).\n", size);
> @@ -802,9 +795,12 @@ static int cbs_av1_split_fragment(CodedBitstreamContext *ctx,
>              goto fail;
>          }
>  
> -        err = cbs_av1_read_leb128(ctx, &gbc, "obu_size", &obu_size);
> -        if (err < 0)
> -            goto fail;
> +        if (header.obu_has_size_field) {
> +            err = cbs_av1_read_leb128(ctx, &gbc, "obu_size", &obu_size);
> +            if (err < 0)
> +                goto fail;
> +        } else
> +            obu_size = size - 1 - header.obu_extension_flag;
>  
>          pos = get_bits_count(&gbc);
>          av_assert0(pos % 8 == 0 && pos / 8 <= size);
> 

LGTM.

Thanks,

- Mark