[FFmpeg-devel] [PATCH 4/6] avformat: add argo_asf muxer

[Zane van Iperen]

On Sun, 2 Aug 2020 14:14:45 +0200
"Andreas Rheinhardt" <andreas.rheinhardt at gmail.com> wrote:

> 
> Zane van Iperen:
> >>> +static int argo_asf_write_trailer(AVFormatContext *s)
> >>> +{
> >>> +    int64_t data_size, num_blocks;
> >>> +
> >>> +    data_size = avio_tell(s->pb) - (ASF_FILE_HEADER_SIZE + ASF_CHUNK_HEADER_SIZE);
> >>> +    num_blocks = data_size / (17 * s->streams[0]->codecpar->channels);
> >>> +
> >>> +    av_assert0(data_size % (17 * s->streams[0]->codecpar->channels) == 0);
> >>
> >> You must not assert this as you have not have any check in place that
> >> guarantees this.
> >>
> >> The comment in the demuxer and the value you assign to num_samples when
> >> writing the header indicates to me that num_samples is supposed to be
> >> always 32; yet there is no check for that in the demuxer and if it is a
> >> value different from 32 and 33, then simply remuxing such a file can
> >> trigger this assert.
> >>
> >
> > You're right, num_samples should always be 32. I will add a check in
> > the demuxer.
> >
> > The 17 comes from "control byte + (32 / 2)" (the frame size for a
> > single channel), so adding that check should guarantee the assertion.
> >
> 
> Why? The packets sent to this muxer need not originate from the demuxer
> via remuxing or from the encoder that you are about to add.

So, something like this basically:

    static int argo_asf_write_packet(AVFormatContext *s, AVPacket *pkt)
    {
        if (pkt->size != 17 && pkt->size != 34)
            return AVERROR(EINVAL);

        avio_write(s->pb, pkt->data, pkt->size);
        return 0;
    }