Re: [FFmpeg-devel] [PATCH] avcodec/bsf/h264_mp4toannexb.c: change extradata to annexb if this is avcc.

[Zhao Zhili <quinkblack-at-foxmail.com@ffmpeg.org>]

> On Apr 24, 2025, at 11:38, jiangjie <jiangjie618@gmail.com> wrote:
> 
> if get AV_PKT_DATA_NEW_EXTRADATA in AVPacket, this bitstream filter will return an error.
> ffmpeg -i rtmp://xxx/live/xxx -bsf:v "h264_mp4toannexb,h264_metadata=aud=remove" -c copy -f null -

H.264 in FLV is avcc. Which service provider use annexb in FLV?

And I don’t think it makes sense to use AV_PKT_DATA_NEW_EXTRADATA together with annexb.

> ---
> libavcodec/bsf/h264_mp4toannexb.c | 26 ++++++++++++++++++++------
> 1 file changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/libavcodec/bsf/h264_mp4toannexb.c b/libavcodec/bsf/h264_mp4toannexb.c
> index dda064287e..4cd002d166 100644
> --- a/libavcodec/bsf/h264_mp4toannexb.c
> +++ b/libavcodec/bsf/h264_mp4toannexb.c
> @@ -252,14 +252,21 @@ static int h264_mp4toannexb_filter_ps(H264BSFContext *s,
>     return 0;
> }
> 
> +static int is_annexb(const uint8_t *extradata, int extra_size) {
> +    if (!extra_size || (extra_size >= 3 && AV_RB24(extradata) == 1) ||
> +        (extra_size >= 4 && AV_RB32(extradata) == 1)) {
> +        return 1;
> +    } else {
> +        return 0;
> +    }
> +}
> +
> static int h264_mp4toannexb_init(AVBSFContext *ctx)
> {
>     int extra_size = ctx->par_in->extradata_size;
> 
>     /* retrieve sps and pps NAL units from extradata */
> -    if (!extra_size                                               ||
> -        (extra_size >= 3 && AV_RB24(ctx->par_in->extradata) == 1) ||
> -        (extra_size >= 4 && AV_RB32(ctx->par_in->extradata) == 1)) {
> +    if (is_annexb(ctx->par_in->extradata, extra_size)) {
>         av_log(ctx, AV_LOG_VERBOSE,
>                "The input looks like it is Annex B already\n");
>     } else if (extra_size >= 7) {
> @@ -294,9 +301,16 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
>     extradata = av_packet_get_side_data(in, AV_PKT_DATA_NEW_EXTRADATA,
>                                         &extradata_size);
>     if (extradata) {
> -        ret = h264_extradata_to_annexb(ctx, extradata, extradata_size);
> -        if (ret < 0)
> -            goto fail;
> +        if (!is_annexb(extradata, extradata_size) && extradata_size >= 7) {
> +            ret = h264_extradata_to_annexb(ctx, extradata, extradata_size);
> +            if (ret < 0)
> +                goto fail;
> +            av_packet_side_data_remove(in->side_data, &in->side_data_elems,
> +                                       AV_PKT_DATA_NEW_EXTRADATA);
> +            av_packet_add_side_data(in, AV_PKT_DATA_NEW_EXTRADATA,
> +                                    ctx->par_out->extradata,
> +                                    ctx->par_out->extradata_size);
> +        }
>     }
> 
>     /* nothing to filter */
> -- 
> 2.49.0
> 
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