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

[Zhao Zhili]

> On Apr 24, 2025, at 13:18, jie jiang <jiangjie618 at gmail.com> wrote:
> 
> fmpeg -i rtmp://xxx/live/xxx -bsf:v
> "h264_mp4toannexb,h264_metadata=aud=remove" -c copy -f null -
> 
> For h264_mp4toannexb, input 264 is avcc,  output is annexb. and for
> h264_metadata, both input and output are annexb.
> If the sps/pps header is updated,  flvdec module will insert
> AV_PKT_DATA_NEW_EXTRADATA to AVPacket and is this format of header is avcc.
> In cbs_bsf_update_side_data function, it will find
> AV_PKT_DATA_NEW_EXTRADATA and this extradata is avcc, that will cause
> h264_metadata to judge that its input is also avcc, but  its input  is from
> h264_mp4toannexb. Using the logic of parsing avcc to parse annexb is
> problematic.
> 
> 

So only remove AV_PKT_DATA_NEW_EXTRADATA can fix the issue?
And the error is from bsf or decoder after h264_mp4toannexb, not h264_mp4toannexb itself, right?

Please share a sample file and add a fate test.

> 
> 
> On Thu, Apr 24, 2025 at 12:19 PM Zhao Zhili <quinkblack at foxmail.com> wrote:
> 
>> 
>> 
>>> On Apr 24, 2025, at 11:38, jiangjie <jiangjie618 at 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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>> 
>> 
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