Re: [FFmpeg-devel] [PATCH] libavformat/mpegtsenc.c -- correctly re-emit extradata ahead of IDR pictures

[Marton Balint <cus@passwd.hu>]

On Tue, 31 Jan 2023, John Coiner wrote:

> This replaces and obsoletes the earlier version of this patch, which had a bug. Thanks to Marton Balint for spotting it.
>
> This fixes https://trac.ffmpeg.org/ticket/10148, it ensures that each IDR frame is prefixed with SPS/PPS.
>
> Tested manually, with inputs containing AUDs (x264's aud=1 mode) and also without (aud=0) to confirm it still inserts AUDs when necessary, and not otherwise.

Your code duplicates AUD-s if they are already present and sps is also 
added:

if original packet had
[AUD][IDR]
it will become 
[AUD][SPS][PPS][AUD][IDR].

Regards,
Marton

>
> ---
> libavformat/mpegtsenc.c | 21 +++++++++++++++------
> 1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
> index 48d39e6a7d..64948f4d75 100644
> --- a/libavformat/mpegtsenc.c
> +++ b/libavformat/mpegtsenc.c
> @@ -1877,6 +1877,7 @@ static int mpegts_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
>
>     if (st->codecpar->codec_id == AV_CODEC_ID_H264) {
>         const uint8_t *p = buf, *buf_end = p + size;
> +        uint8_t found_aud = 0;
>         uint32_t state = -1;
>         int extradd = (pkt->flags & AV_PKT_FLAG_KEY) ? st->codecpar->extradata_size : 0;
>         int ret = ff_check_h264_startcode(s, st, pkt);
> @@ -1886,17 +1887,25 @@ static int mpegts_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
>         if (extradd && AV_RB24(st->codecpar->extradata) > 1)
>             extradd = 0;
>
> +        // Ensure that all pictures are prefixed with an AUD, and that
> +        // IDR pictures are also prefixed with SPS and PPS. SPS and PPS
> +        // are assumed to be available in 'extradata' if not found in-band.
>         do {
>             p = avpriv_find_start_code(p, buf_end, &state);
>             av_log(s, AV_LOG_TRACE, "nal %"PRId32"\n", state & 0x1f);
> -            if ((state & 0x1f) == 7)
> +            if ((state & 0x1f) == 7)  // SPS NAL
>                 extradd = 0;
> -        } while (p < buf_end && (state & 0x1f) != 9 &&
> -                 (state & 0x1f) != 5 && (state & 0x1f) != 1);
> -
> -        if ((state & 0x1f) != 5)
> +            if ((state & 0x1f) == 9)  // AUD
> +                found_aud = 1;
> +        } while (p < buf_end
> +                 && (state & 0x1f) != 5  // IDR picture
> +                 && (state & 0x1f) != 1  // non-IDR picture
> +                 && (extradd > 0 || !found_aud));
> +        if ((state & 0x1f) != 5) {
> +            // Did not find IDR picture; do not emit extradata.
>             extradd = 0;
> -        if ((state & 0x1f) != 9) { // AUD NAL
> +        }
> +        if (extradd > 0 || !found_aud) {
>             data = av_malloc(pkt->size + 6 + extradd);
>             if (!data)
>                 return AVERROR(ENOMEM);
> -- 
> 2.39.1.456.gfc5497dd1b-goog
>
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