avformat/mov: Add support for still image AVIF parsing

This patch supports AVIF still images conforming to the
final specification that have exactly one item (i.e. no alpha channel).
The iloc box is parsed and the mov index populated.

Partially fixes #7621.

Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
Signed-off-by: Gyan Doshi <ffmpeg@gyani.pro>

libavformat/isom.h

@@ -316,6 +316,7 @@ 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);

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);
 
@@ -7431,6 +7432,145 @@ 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) {
+        av_log(c->fc, AV_LOG_ERROR, "iloc: index_size != 0 not supported.\n");
+        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.
+        av_log(c->fc, AV_LOG_ERROR, "iloc: item_count > 1 not supported.\n");
+        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.
+            av_log(c->fc, AV_LOG_ERROR, "iloc: extent_count > 1 not supported.\n");
+            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 },
@@ -7533,6 +7673,7 @@ 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 }
 };