Re: [FFmpeg-devel] [PATCH 3/3] avformat/movenc: Add support for AVIF muxing

[Vignesh Venkatasubramanian <vigneshv-at-google.com@ffmpeg.org>]

On Wed, Apr 13, 2022 at 2:01 PM Andreas Rheinhardt
<andreas.rheinhardt@outlook.com> wrote:
>
> Vignesh Venkatasubramanian:
> > Add an AVIF muxer by re-using the existing the mov/mp4 muxer.
> >
> > AVIF Specification: https://aomediacodec.github.io/av1-avif
> >
> > Sample usage for still image:
> > ffmpeg -i image.png -c:v libaom-av1 -avif-image 1 image.avif
> >
> > Sample usage for animated AVIF image:
> > ffmpeg -i video.mp4 animated.avif
> >
> > We can re-use any of the AV1 encoding options that will make
> > sense for image encoding (like bitrate, tiles, encoding speed,
> > etc).
> >
> > The files generated by this muxer has been verified to be valid
> > AVIF files by the following:
> > 1) Displays on Chrome (both still and animated images).
> > 2) Displays on Firefox (only still images, firefox does not support
> >    animated AVIF yet).
> > 3) Verified to be valid by Compliance Warden:
> >    https://github.com/gpac/ComplianceWarden
> >
> > Fixes the encoder/muxer part of Trac Ticket #7621
> >
> > Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
> > ---
> >  configure                |   1 +
> >  libavformat/allformats.c |   1 +
> >  libavformat/movenc.c     | 337 ++++++++++++++++++++++++++++++++++++---
> >  libavformat/movenc.h     |   5 +
> >  4 files changed, 319 insertions(+), 25 deletions(-)
> >
> > +static int avif_write_trailer(AVFormatContext *s)
> > +{
> > +    AVIOContext *pb = s->pb;
> > +    MOVMuxContext *mov = s->priv_data;
> > +    int64_t pos_backup, mdat_pos;
> > +    uint8_t *buf;
> > +    int buf_size, moov_size;
> > +
> > +    if (mov->moov_written) return 0;
>
> Can it happen that moov_written is true? What happens if it is? (I
> presume the file to be invalid.)
>

This is more of a sanity check. I don't think this will ever happen
(as long as write_trailer is not called more than once). If you
prefer, i can remove it.

> > +
> > +    mov->is_animated_avif = s->streams[0]->nb_frames > 1;
> > +    mov_write_identification(pb, s);
> > +    mov_write_meta_tag(pb, mov, s);
> > +
> > +    moov_size = get_moov_size(s);
> > +    mov->tracks[0].data_offset = avio_tell(pb) + moov_size + 8;
> > +
> > +    if (mov->is_animated_avif) {
> > +        int ret;
> > +        if ((ret = mov_write_moov_tag(pb, mov, s)) < 0)
> > +            return ret;
> > +    }
> > +
> > +    buf_size = avio_get_dyn_buf(mov->mdat_buf, &buf);
> > +    avio_wb32(pb, buf_size + 8);
> > +    ffio_wfourcc(pb, "mdat");
> > +    mdat_pos = avio_tell(pb);
> > +
> > +    if (mdat_pos != (uint32_t)mdat_pos) {
> > +        av_log(s, AV_LOG_ERROR, "mdat offset does not fit in 32 bits\n");
> > +        return AVERROR_INVALIDDATA;
> > +    }
> > +
> > +    avio_write(pb, buf, buf_size);
> > +
> > +    // write extent offset.
> > +    pos_backup = avio_tell(pb);
> > +    avio_seek(pb, mov->avif_extent_pos, SEEK_SET);
> > +    avio_wb32(pb, mdat_pos); /* rewrite offset */
> > +    avio_seek(pb, pos_backup, SEEK_SET);
> > +
> > +    return 0;
> > +}
> > +
>
> - Andreas
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-- 
Vignesh
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