Re: [FFmpeg-devel] [PATCH] avformat/mov: Add support for still image AVIF parsing

[Paul B Mahol <onemda@gmail.com>]

On Tue, Apr 19, 2022 at 10:57 PM Vignesh Venkatasubramanian <
vigneshv-at-google.com@ffmpeg.org> wrote:

> Add support for parsing AVIF still images. This patches supports
> AVIF still images that have exactly 1 item (i.e.) no alpha channel.
> Essentially, we will have to parse the "iloc" box and populate
> the mov index.
>
> With this patch, we can decode still AVIF images like so:
> ffmpeg -i image.avif image.png
>
> Partially fixes trac ticket #7621
>

LGTM


>
> Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
> ---
>  libavformat/isom.h |   1 +
>  libavformat/mov.c  | 137 +++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 138 insertions(+)
>
> diff --git a/libavformat/isom.h b/libavformat/isom.h
> index 5caf42b15d..02d681e3ae 100644
> --- a/libavformat/isom.h
> +++ b/libavformat/isom.h
> @@ -315,6 +315,7 @@ typedef struct MOVContext {
>      int have_read_mfra_size;
>      uint32_t mfra_size;
>      uint32_t max_stts_delta;
> +    int is_still_picture_avif;
>  } MOVContext;
>
>  int ff_mp4_read_descr_len(AVIOContext *pb);
> diff --git a/libavformat/mov.c b/libavformat/mov.c
> index 6c847de164..e925690584 100644
> --- a/libavformat/mov.c
> +++ b/libavformat/mov.c
> @@ -1136,6 +1136,7 @@ static int mov_read_ftyp(MOVContext *c, AVIOContext
> *pb, MOVAtom atom)
>          c->isom = 1;
>      av_log(c->fc, AV_LOG_DEBUG, "ISO: File Type Major Brand:
> %.4s\n",(char *)&type);
>      av_dict_set(&c->fc->metadata, "major_brand", type, 0);
> +    c->is_still_picture_avif = !strncmp(type, "avif", 4);
>      minor_ver = avio_rb32(pb); /* minor version */
>      av_dict_set_int(&c->fc->metadata, "minor_version", minor_ver, 0);
>
> @@ -7430,6 +7431,141 @@ static int mov_read_SAND(MOVContext *c,
> AVIOContext *pb, MOVAtom atom)
>      return 0;
>  }
>
> +static int rb_size(AVIOContext *pb, uint64_t* value, int size)
> +{
> +    if (size == 0)
> +        *value = 0;
> +    else if (size == 1)
> +        *value = avio_r8(pb);
> +    else if (size == 2)
> +        *value = avio_rb16(pb);
> +    else if (size == 4)
> +        *value = avio_rb32(pb);
> +    else if (size == 8)
> +        *value = avio_rb64(pb);
> +    else
> +        return -1;
> +    return size;
> +}
> +
> +static int mov_read_iloc(MOVContext *c, AVIOContext *pb, MOVAtom atom)
> +{
> +    int version, offset_size, length_size, base_offset_size, index_size;
> +    int item_count, extent_count;
> +    uint64_t base_offset, extent_offset, extent_length;
> +    uint8_t value;
> +    AVStream *st;
> +    MOVStreamContext *sc;
> +
> +    if (!c->is_still_picture_avif) {
> +        // * For non-avif, we simply ignore the iloc box.
> +        // * For animated avif, we don't care about the iloc box as all
> the
> +        //   necessary information can be found in the moov box.
> +        return 0;
> +    }
> +
> +    if (c->fc->nb_streams) {
> +        av_log(c->fc, AV_LOG_INFO, "Duplicate iloc box found\n");
> +        return 0;
> +    }
> +
> +    st = avformat_new_stream(c->fc, NULL);
> +    if (!st)
> +        return AVERROR(ENOMEM);
> +    st->id = c->fc->nb_streams;
> +    sc = av_mallocz(sizeof(MOVStreamContext));
> +    if (!sc)
> +        return AVERROR(ENOMEM);
> +
> +    st->priv_data = sc;
> +    st->codecpar->codec_type = AVMEDIA_TYPE_VIDEO;
> +    st->codecpar->codec_id = AV_CODEC_ID_AV1;
> +    sc->ffindex = st->index;
> +    c->trak_index = st->index;
> +    st->avg_frame_rate.num = st->avg_frame_rate.den = 1;
> +    st->time_base.num = st->time_base.den = 1;
> +    st->nb_frames = 1;
> +    sc->time_scale = 1;
> +    sc = st->priv_data;
> +    sc->pb = c->fc->pb;
> +    sc->pb_is_copied = 1;
> +
> +    version = avio_r8(pb);
> +    avio_rb24(pb);  // flags.
> +
> +    value = avio_r8(pb);
> +    offset_size = (value >> 4) & 0xF;
> +    length_size = value & 0xF;
> +    value = avio_r8(pb);
> +    base_offset_size = (value >> 4) & 0xF;
> +    index_size = !version ? 0 : (value & 0xF);
> +    if (index_size)
> +        return AVERROR_PATCHWELCOME;
> +    item_count = (version < 2) ? avio_rb16(pb) : avio_rb32(pb);
> +    if (item_count > 1) {
> +        // For still AVIF images, we only support one item. Second item
> will
> +        // generally be found for AVIF images with alpha channel. We don't
> +        // support them as of now.
> +        return AVERROR_PATCHWELCOME;
> +    }
> +
> +    // Populate the necessary fields used by mov_build_index.
> +    sc->stsc_count = item_count;
> +    sc->stsc_data = av_malloc_array(item_count, sizeof(*sc->stsc_data));
> +    if (!sc->stsc_data)
> +        return AVERROR(ENOMEM);
> +    sc->stsc_data[0].first = 1;
> +    sc->stsc_data[0].count = 1;
> +    sc->stsc_data[0].id = 1;
> +    sc->chunk_count = item_count;
> +    sc->chunk_offsets =
> +        av_malloc_array(item_count, sizeof(*sc->chunk_offsets));
> +    if (!sc->chunk_offsets)
> +        return AVERROR(ENOMEM);
> +    sc->sample_count = item_count;
> +    sc->sample_sizes =
> +        av_malloc_array(item_count, sizeof(*sc->sample_sizes));
> +    if (!sc->sample_sizes)
> +        return AVERROR(ENOMEM);
> +    sc->stts_count = item_count;
> +    sc->stts_data = av_malloc_array(item_count, sizeof(*sc->stts_data));
> +    if (!sc->stts_data)
> +        return AVERROR(ENOMEM);
> +    sc->stts_data[0].count = 1;
> +    // Not used for still images. But needed by mov_build_index.
> +    sc->stts_data[0].duration = 0;
> +
> +    for (int i = 0; i < item_count; i++) {
> +        (version < 2) ? avio_rb16(pb) : avio_rb32(pb);  // item_id;
> +        if (version > 0)
> +            avio_rb16(pb);  // construction_method.
> +        avio_rb16(pb);  // data_reference_index.
> +        if (rb_size(pb, &base_offset, base_offset_size) < 0)
> +            return AVERROR_INVALIDDATA;
> +        extent_count = avio_rb16(pb);
> +        if (extent_count > 1) {
> +            // For still AVIF images, we only support one extent item.
> +            return AVERROR_PATCHWELCOME;
> +        }
> +        for (int j = 0; j < extent_count; j++) {
> +            if (rb_size(pb, &extent_offset, offset_size) < 0 ||
> +                rb_size(pb, &extent_length, length_size) < 0)
> +                return AVERROR_INVALIDDATA;
> +            sc->sample_sizes[0] = extent_length;
> +            sc->chunk_offsets[0] = base_offset + extent_offset;
> +        }
> +    }
> +
> +    mov_build_index(c, st);
> +
> +    // For still AVIF images, the iloc box contains all the necessary
> +    // information that would generally be provided by the moov box. So
> simply
> +    // mark that we have found the moov box so that parsing can continue.
> +    c->found_moov = 1;
> +
> +    return atom.size;
> +}
> +
>  static const MOVParseTableEntry mov_default_parse_table[] = {
>  { MKTAG('A','C','L','R'), mov_read_aclr },
>  { MKTAG('A','P','R','G'), mov_read_avid },
> @@ -7532,6 +7668,7 @@ static const MOVParseTableEntry
> mov_default_parse_table[] = {
>  { MKTAG('k','i','n','d'), mov_read_kind },
>  { MKTAG('S','A','3','D'), mov_read_SA3D }, /* ambisonic audio box */
>  { MKTAG('S','A','N','D'), mov_read_SAND }, /* non diegetic audio box */
> +{ MKTAG('i','l','o','c'), mov_read_iloc },
>  { 0, NULL }
>  };
>
> --
> 2.36.0.rc0.470.gd361397f0d-goog
>
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