Re: [FFmpeg-devel] [PATCH] avcodec/h264_mp4toannexb: Prepend SPS/PPS to buffering period SEI

[Anton Khirnov <anton@khirnov.net>]

Quoting Josh Allmann (2024-07-09 21:05:47)
> Encoders may emit a buffering period SEI without a corresponding
> SPS/PPS if the SPS/PPS is carried out-of-band, eg with avcc.
> 
> During Annex B conversion, this may result in the SPS/PPS being
> inserted *after* the buffering period SEI but before the IDR NAL.
> 
> Since the buffering period SEI references the SPS, the SPS/PPS
> needs to come first.
> ---
> 
> Notes:
>     v2: Updated FATE test refs
> 
>  libavcodec/bsf/h264_mp4toannexb.c          | 13 +++++++++++++
>  tests/ref/fate/h264-bsf-mp4toannexb        |  2 +-
>  tests/ref/fate/h264_mp4toannexb_ticket2991 | 18 +++++++++---------
>  tests/ref/fate/segment-mp4-to-ts           | 12 ++++++------
>  4 files changed, 29 insertions(+), 16 deletions(-)
> 
> diff --git a/libavcodec/bsf/h264_mp4toannexb.c b/libavcodec/bsf/h264_mp4toannexb.c
> index 92af6a6881..6607f1e91a 100644
> --- a/libavcodec/bsf/h264_mp4toannexb.c
> +++ b/libavcodec/bsf/h264_mp4toannexb.c
> @@ -363,6 +363,19 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
>              if (!new_idr && unit_type == H264_NAL_IDR_SLICE && (buf[1] & 0x80))
>                  new_idr = 1;
>  
> +            /* If this is a buffering period SEI without a corresponding sps/pps
> +             * then prepend any existing sps/pps before the SEI */
> +            if (unit_type == H264_NAL_SEI && buf[1] == 0 && !sps_seen && !pps_seen) {

That 0 should be SEI_TYPE_BUFFERING_PERIOD, right?

> +                if (s->sps_size) {
> +                    count_or_copy(&out, &out_size, s->sps, s->sps_size, PS_OUT_OF_BAND, j);
> +                    sps_seen = 1;
> +                }
> +                if (s->pps_size) {
> +                    count_or_copy(&out, &out_size, s->pps, s->pps_size, PS_OUT_OF_BAND, j);
> +                    pps_seen = 1;
> +                }

Is there a reason to insert the PPS? IIUC only the SPS is needed.

-- 
Anton Khirnov
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