Function avifEncoderWriteTrackMetaBox

src/write.c:856–924

Write unassociated metadata items (EXIF, XMP) to a small meta box inside of a trak box. These items are implicitly associated with the track they are contained within.

// Write unassociated metadata items (EXIF, XMP) to a small meta box inside of a trak box.
// These items are implicitly associated with the track they are contained within.
static avifResult avifEncoderWriteTrackMetaBox(avifEncoder * encoder, avifRWStream * s)
{
    // Count how many non-image items (such as EXIF/XMP) are being written
    uint32_t metadataItemCount = 0;
    for (uint32_t itemIndex = 0; itemIndex < encoder->data->items.count; ++itemIndex) {
        avifEncoderItem * item = &encoder->data->items.item[itemIndex];
        if (memcmp(item->type, encoder->data->imageItemType, 4) != 0) {
            ++metadataItemCount;
        }
    }
    if (metadataItemCount == 0) {
        // Don't even bother writing the trak meta box
        return AVIF_RESULT_OK;
    }

    avifBoxMarker meta;
    AVIF_CHECKRES(avifRWStreamWriteFullBox(s, "meta", AVIF_BOX_SIZE_TBD, 0, 0, &meta));

    AVIF_CHECKRES(avifRWStreamWriteHandlerBox(s, "pict"));

    avifBoxMarker iloc;
    AVIF_CHECKRES(avifRWStreamWriteFullBox(s, "iloc", AVIF_BOX_SIZE_TBD, 0, 0, &iloc));
    AVIF_CHECKRES(avifRWStreamWriteBits(s, 4, /*bitCount=*/4));          // unsigned int(4) offset_size;
    AVIF_CHECKRES(avifRWStreamWriteBits(s, 4, /*bitCount=*/4));          // unsigned int(4) length_size;
    AVIF_CHECKRES(avifRWStreamWriteBits(s, 0, /*bitCount=*/4));          // unsigned int(4) base_offset_size;
    AVIF_CHECKRES(avifRWStreamWriteBits(s, 0, /*bitCount=*/4));          // unsigned int(4) reserved;
    AVIF_CHECKRES(avifRWStreamWriteU16(s, (uint16_t)metadataItemCount)); // unsigned int(16) item_count;
    for (uint32_t trakItemIndex = 0; trakItemIndex < encoder->data->items.count; ++trakItemIndex) {
        avifEncoderItem * item = &encoder->data->items.item[trakItemIndex];
        if (memcmp(item->type, encoder->data->imageItemType, 4) == 0) {
            // Skip over all non-metadata items
            continue;
        }

        AVIF_CHECKRES(avifRWStreamWriteU16(s, item->id));          // unsigned int(16) item_ID;
        AVIF_CHECKRES(avifRWStreamWriteU16(s, 0));                 // unsigned int(16) data_reference_index;
        AVIF_CHECKRES(avifRWStreamWriteU16(s, 1));                 // unsigned int(16) extent_count;
        AVIF_CHECKRES(avifEncoderItemAddMdatFixup(item, s));       //
        AVIF_CHECKRES(avifRWStreamWriteU32(s, 0 /* set later */)); // unsigned int(offset_size*8) extent_offset;
        AVIF_CHECKRES(avifRWStreamWriteU32(s, (uint32_t)item->metadataPayload.size)); // unsigned int(length_size*8) extent_length;
    }
    AVIF_CHECKRES(avifRWStreamFinishBox(s, iloc));

    avifBoxMarker iinf;
    AVIF_CHECKRES(avifRWStreamWriteFullBox(s, "iinf", AVIF_BOX_SIZE_TBD, 0, 0, &iinf));
    AVIF_CHECKRES(avifRWStreamWriteU16(s, (uint16_t)metadataItemCount)); //  unsigned int(16) entry_count;
    for (uint32_t trakItemIndex = 0; trakItemIndex < encoder->data->items.count; ++trakItemIndex) {
        avifEncoderItem * item = &encoder->data->items.item[trakItemIndex];
        if (memcmp(item->type, encoder->data->imageItemType, 4) == 0) {
            continue;
        }

        AVIF_ASSERT_OR_RETURN(!item->hiddenImage);
        avifBoxMarker infe;
        AVIF_CHECKRES(avifRWStreamWriteFullBox(s, "infe", AVIF_BOX_SIZE_TBD, 2, 0, &infe));
        AVIF_CHECKRES(avifRWStreamWriteU16(s, item->id));                             // unsigned int(16) item_ID;
        AVIF_CHECKRES(avifRWStreamWriteU16(s, 0));                                    // unsigned int(16) item_protection_index;
        AVIF_CHECKRES(avifRWStreamWrite(s, item->type, 4));                           // unsigned int(32) item_type;