On Wed, May 18, 2022 at 2:56 PM Vignesh Venkatasubramanian <vigneshv-at-google....@ffmpeg.org> wrote: > > AVIF specification allows for alpha channel as an auxillary item (in
auxiliary > case of still images) or as an auxillary track (in case of animated > images). Add support for both of these. The AVIF muxer will take > exactly two streams (when alpha is present) as input (first one being > the YUV planes and the second one being the alpha plane). > > The input has to come from two different images (one of it color and > the other one being alpha), or it can come from a single file > source with the alpha channel extracted using the "alphaextract" > filter. > > Example using alphaextract: > ffmpeg -i rgba.png -filter_complex "[0:v]alphaextract[a]" -map 0 -map "[a]" > -still-picture 1 avif_with_alpha.avif > > Example using two sources (first source can be in any pixel format and > the second source has to be in monochrome grey pixel format): > ffmpeg -i color.avif -i grey.avif -map 0 -map 1 -c copy avif_with_alpha.avif > > The generated files pass the compliance checks in Compliance Warden: > https://github.com/gpac/ComplianceWarden > > libavif (the reference avif library) is able to decode the files > generated using this patch. > > They also play back properly (with transparent background) in: > 1) Chrome > 2) Firefox (only still AVIF, no animation support) > > Signed-off-by: Vignesh Venkatasubramanian <vigne...@google.com> > --- > libavformat/movenc.c | 185 +++++++++++++++++++++++++++++-------------- > libavformat/movenc.h | 4 +- > 2 files changed, 128 insertions(+), 61 deletions(-) > > diff --git a/libavformat/movenc.c b/libavformat/movenc.c > index de971f94e8..00e42b7abb 100644 > --- a/libavformat/movenc.c > +++ b/libavformat/movenc.c > @@ -2852,7 +2852,7 @@ static int mov_write_hdlr_tag(AVFormatContext *s, > AVIOContext *pb, MOVTrack *tra > hdlr = (track->mode == MODE_MOV) ? "mhlr" : "\0\0\0\0"; > if (track->par->codec_type == AVMEDIA_TYPE_VIDEO) { > if (track->mode == MODE_AVIF) { > - hdlr_type = "pict"; > + hdlr_type = (track == &mov->tracks[0]) ? "pict" : "auxv"; > descr = "PictureHandler"; > } else { > hdlr_type = "vide"; > @@ -2940,57 +2940,83 @@ static int mov_write_iloc_tag(AVIOContext *pb, > MOVMuxContext *mov, AVFormatConte > avio_wb32(pb, 0); /* Version & flags */ > avio_w8(pb, (4 << 4) + 4); /* offset_size(4) and length_size(4) */ > avio_w8(pb, 0); /* base_offset_size(4) and reserved(4) */ > - avio_wb16(pb, 1); /* item_count */ > + avio_wb16(pb, s->nb_streams); /* item_count */ This assumes at most 2 streams for AVIF, the use of nb_streams here and elsewhere carry any risk for other formats? > [...] > > @@ -6874,14 +6920,23 @@ static int mov_init(AVFormatContext *s) > > /* AVIF output must have exactly one video stream */ This is no longer true. > if (mov->mode == MODE_AVIF) { > - if (s->nb_streams > 1) { > - av_log(s, AV_LOG_ERROR, "AVIF output requires exactly one > stream\n"); > + if (s->nb_streams > 2) { > + av_log(s, AV_LOG_ERROR, "AVIF output requires exactly one or two > streams\n"); > return AVERROR(EINVAL); > } > - if (s->streams[0]->codecpar->codec_type != AVMEDIA_TYPE_VIDEO) { > - av_log(s, AV_LOG_ERROR, "AVIF output requires one video > stream\n"); > + if (s->streams[0]->codecpar->codec_type != AVMEDIA_TYPE_VIDEO && > + (s->nb_streams > 1 && s->streams[1]->codecpar->codec_type != > AVMEDIA_TYPE_VIDEO)) { > + av_log(s, AV_LOG_ERROR, "AVIF output supports only video > streams\n"); > return AVERROR(EINVAL); > } > + if (s->nb_streams > 1) { > + const AVPixFmtDescriptor *pixdesc = > + av_pix_fmt_desc_get(s->streams[1]->codecpar->format); > + if (pixdesc->nb_components != 1) { > + av_log(s, AV_LOG_ERROR, "Second stream for AVIF (alpha) > output must have exactly one plane\n"); > + return AVERROR(EINVAL); > + } > + } > s->streams[0]->disposition |= AV_DISPOSITION_DEFAULT; > } > > @@ -7543,18 +7598,25 @@ static int avif_write_trailer(AVFormatContext *s) > { > AVIOContext *pb = s->pb; > MOVMuxContext *mov = s->priv_data; > - int64_t pos_backup, mdat_pos; > + int64_t pos_backup, extent_offsets[2]; > uint8_t *buf; > - int buf_size, moov_size; > + int buf_size, moov_size, i; > > if (mov->moov_written) return 0; > > mov->is_animated_avif = s->streams[0]->nb_frames > 1; > + if (mov->is_animated_avif && s->nb_streams > 1) { > + // For animated avif with alpha channel, we need to write a the tref ...write a tref... _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".