Re: [FFmpeg-devel] [PATCH] hevcdec: skip slices with missing PPS instead of skipping the entire packet

[James Almer <jamrial@gmail.com>]

On 12/28/2021 10:49 AM, Hendrik Leppkes wrote:
> Aborting decoding of the entire packet on a missing PPS can result in
> missing the actual PPS on streams with badly ordered NALs, where the
> SPS/PPS/VPS are stitched to the back of the previous frame, instead of
> the beginning of the next frame.
> 
> Instead, skip the undecodable slice, and let the decoder process further
> NALs in the same packet.
> ---
>   libavcodec/hevcdec.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/hevcdec.c b/libavcodec/hevcdec.c
> index 3aa70e2245..c2451d682e 100644
> --- a/libavcodec/hevcdec.c
> +++ b/libavcodec/hevcdec.c
> @@ -575,7 +575,7 @@ static int hls_slice_header(HEVCContext *s)
>       sh->pps_id = get_ue_golomb_long(gb);
>       if (sh->pps_id >= HEVC_MAX_PPS_COUNT || !s->ps.pps_list[sh->pps_id]) {
>           av_log(s->avctx, AV_LOG_ERROR, "PPS id out of range: %d\n", sh->pps_id);
> -        return AVERROR_INVALIDDATA;
> +        return 1; // skip slice with missing PPS

The decoder should IMO also set the output frame's decode_error_flags to 
FF_DECODE_ERROR_DECODE_SLICES in this scenario.

>       }
>       if (!sh->first_slice_in_pic_flag &&
>           s->ps.pps != (HEVCPPS*)s->ps.pps_list[sh->pps_id]->data) {
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