Function avifParseCodecConfiguration

src/read.c:2651–2699

Implementation of section 2.3.3 of AV1 Codec ISO Media File Format Binding specification v1.2.0. See https://aomediacodec.github.io/av1-isobmff/v1.2.0.html#av1codecconfigurationbox-syntax.

// Implementation of section 2.3.3 of AV1 Codec ISO Media File Format Binding specification v1.2.0.
// See https://aomediacodec.github.io/av1-isobmff/v1.2.0.html#av1codecconfigurationbox-syntax.
static avifBool avifParseCodecConfiguration(avifROStream * s, avifCodecConfigurationBox * config, const char * configPropName, avifDiagnostics * diag)
{
    const size_t av1COffset = avifROStreamOffset(s);

    uint32_t marker, version;
    AVIF_CHECK(avifROStreamReadBitsU32(s, &marker, /*bitCount=*/1)); // unsigned int (1) marker = 1;
    if (!marker) {
        avifDiagnosticsPrintf(diag, "%.4s contains illegal marker: [%u]", configPropName, marker);
        return AVIF_FALSE;
    }
    AVIF_CHECK(avifROStreamReadBitsU32(s, &version, /*bitCount=*/7)); // unsigned int (7) version = 1;
    if (version != 1) {
        avifDiagnosticsPrintf(diag, "%.4s contains illegal version: [%u]", configPropName, version);
        return AVIF_FALSE;
    }

    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->seqProfile, /*bitCount=*/3));         // unsigned int (3) seq_profile;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->seqLevelIdx0, /*bitCount=*/5));       // unsigned int (5) seq_level_idx_0;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->seqTier0, /*bitCount=*/1));           // unsigned int (1) seq_tier_0;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->highBitdepth, /*bitCount=*/1));       // unsigned int (1) high_bitdepth;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->twelveBit, /*bitCount=*/1));          // unsigned int (1) twelve_bit;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->monochrome, /*bitCount=*/1));         // unsigned int (1) monochrome;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->chromaSubsamplingX, /*bitCount=*/1)); // unsigned int (1) chroma_subsampling_x;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->chromaSubsamplingY, /*bitCount=*/1)); // unsigned int (1) chroma_subsampling_y;
    AVIF_CHECK(avifROStreamReadBitsU8(s, &config->chromaSamplePosition, /*bitCount=*/2)); // unsigned int (2) chroma_sample_position;

    // unsigned int (3) reserved = 0;
    // unsigned int (1) initial_presentation_delay_present;
    // if (initial_presentation_delay_present) {
    //   unsigned int (4) initial_presentation_delay_minus_one;
    // } else {
    //   unsigned int (4) reserved = 0;
    // }
    AVIF_CHECK(avifROStreamSkip(s, /*byteCount=*/1));

    // According to section 2.2.1 of AV1 Image File Format specification v1.1.0:
    //   - Sequence Header OBUs should not be present in the AV1CodecConfigurationBox.
    //   - If a Sequence Header OBU is present in the AV1CodecConfigurationBox,
    //     it shall match the Sequence Header OBU in the AV1 Image Item Data.
    //   - Metadata OBUs, if present, shall match the values given in other item properties,
    //     such as the PixelInformationProperty or ColourInformationBox.
    // See https://aomediacodec.github.io/av1-avif/v1.1.0.html#av1-configuration-item-property.
    // For simplicity, the constraints above are not enforced.
    // The following is skipped by avifParseItemPropertyContainerBox().
    // unsigned int (8) configOBUs[];

    AVIF_CHECK(avifROStreamOffset(s) - av1COffset == 4); // Make sure avifParseCodecConfiguration() reads exactly 4 bytes.
    return AVIF_TRUE;
}

static avifBool avifParseCodecConfigurationBoxProperty(avifProperty * prop,
                                                       const uint8_t * raw,