Function avifEncoderWriteMiniBox

src/write.c:2509–2859

}

static avifResult avifEncoderWriteMiniBox(avifEncoder * encoder, avifRWStream * s)
{
    const avifEncoderItem * colorItem = NULL;
    const avifEncoderItem * alphaItem = NULL;
    const avifEncoderItem * gainmapItem = NULL;
    for (uint32_t itemIndex = 0; itemIndex < encoder->data->items.count; ++itemIndex) {
        avifEncoderItem * item = &encoder->data->items.item[itemIndex];
        if (item->id == encoder->data->primaryItemID) {
            AVIF_ASSERT_OR_RETURN(!colorItem);
            colorItem = item;
        } else if (item->itemCategory == AVIF_ITEM_ALPHA && item->irefToID == encoder->data->primaryItemID) {
            AVIF_ASSERT_OR_RETURN(!alphaItem);
            alphaItem = item;
        }
        if (item->itemCategory == AVIF_ITEM_GAIN_MAP) {
            AVIF_ASSERT_OR_RETURN(!gainmapItem);
            gainmapItem = item;
        }
    }

    AVIF_ASSERT_OR_RETURN(colorItem);
    const avifRWData * colorData = &colorItem->encodeOutput->samples.sample[0].data;
    const avifRWData * alphaData = alphaItem ? &alphaItem->encodeOutput->samples.sample[0].data : NULL;
    const avifRWData * gainmapData = gainmapItem ? &gainmapItem->encodeOutput->samples.sample[0].data : NULL;

    const avifImage * const image = encoder->data->imageMetadata;

    const avifBool hasAlpha = alphaItem != NULL;
    const avifBool alphaIsPremultiplied = encoder->data->imageMetadata->alphaPremultiplied;
    const avifBool hasGainmap = gainmapItem != NULL;
    const avifBool hasHdr = hasGainmap; // libavif only supports gainmap-based HDR encoding for now.
    const avifBool hasIcc = image->icc.size != 0;
    const uint32_t chromaSubsampling = image->yuvFormat == AVIF_PIXEL_FORMAT_YUV400   ? 0
                                       : image->yuvFormat == AVIF_PIXEL_FORMAT_YUV420 ? 1
                                       : image->yuvFormat == AVIF_PIXEL_FORMAT_YUV422 ? 2
                                                                                      : 3;

    const avifColorPrimaries defaultColorPrimaries = hasIcc ? AVIF_COLOR_PRIMARIES_UNSPECIFIED : AVIF_COLOR_PRIMARIES_BT709;
    const avifTransferCharacteristics defaultTransferCharacteristics = hasIcc ? AVIF_TRANSFER_CHARACTERISTICS_UNSPECIFIED
                                                                              : AVIF_TRANSFER_CHARACTERISTICS_SRGB;
    const avifMatrixCoefficients defaultMatrixCoefficients = chromaSubsampling == 0 ? AVIF_MATRIX_COEFFICIENTS_UNSPECIFIED
                                                                                    : AVIF_MATRIX_COEFFICIENTS_BT601;
    const avifBool hasExplicitCicp = image->colorPrimaries != defaultColorPrimaries ||
                                     image->transferCharacteristics != defaultTransferCharacteristics ||
                                     image->matrixCoefficients != defaultMatrixCoefficients;

    const avifBool floatFlag = AVIF_FALSE;
    const avifBool fullRange = image->yuvRange == AVIF_RANGE_FULL;

    // In AV1, the chroma_sample_position syntax element is not present for the YUV 4:2:2 format.
    // Assume that AV1 uses the same 4:2:2 chroma sample location as HEVC and VVC (colocated).
    if (image->yuvFormat != AVIF_PIXEL_FORMAT_YUV420 && image->yuvChromaSamplePosition != AVIF_CHROMA_SAMPLE_POSITION_UNKNOWN) {
        avifDiagnosticsPrintf(&encoder->diag,
                              "YUV chroma sample position %d is only supported with 4:2:0 YUV format in AV1",
                              image->yuvChromaSamplePosition);
        return AVIF_RESULT_INVALID_ARGUMENT;
    }
    // For the YUV 4:2:0 format, assume centered sample position unless specified otherwise.