Function aomCodecEncodeImage

src/codec_aom.c:656–1348

}

static avifResult aomCodecEncodeImage(avifCodec * codec,
                                      avifEncoder * encoder,
                                      const avifImage * image,
                                      avifBool alpha,
                                      int tileRowsLog2,
                                      int tileColsLog2,
                                      int quality,
                                      avifEncoderChanges encoderChanges,
                                      avifBool disableLaggedOutput,
                                      avifAddImageFlags addImageFlags,
                                      avifCodecEncodeOutput * output)
{
    // Save the quality of the first layer because it's useful for further decision making
    if (encoder->extraLayerCount > 0 && codec->internal->currentLayer == 0) {
        codec->internal->qualityFirstLayer = quality;
    }

    // Determine whether the encoder should be configured to use intra frames only, either by setting aomUsage to
    // AOM_USAGE_ALL_INTRA, or by manually configuring the encoder so all frames will be key frames (if AOM_USAGE_ALL_INTRA isn't
    // available).

    // For libaom versions older than 3.14.0, all-intra encoding is beneficial when encoding a two-layer image item and the
    // quality of the first layer is very low. Switching to all-intra encoding comes with the following benefits:
    // - The first layer will be smaller than the second layer (which is often not the case with inter encoding)
    // - Outputs have predictable file sizes: the sum of the first layer (quality <= 10) plus the second layer (quality set by
    //   the caller)
    // - Because the first layer is very small, layered encoding overhead is also smaller and more stable (about 5-8% for quality
    //   40 and 2-4% for quality 60)
    // Note: libaom 3.14.0 introduces a mechanism to completely control each layer's QP, and extends tune IQ to inter-frame
    // encoding modes (AOM_USAGE_GOOD_QUALITY and AOM_USAGE_REALTIME), so there's no need to use all-intra encoding for layered.

    // aom_codec.h says: aom_codec_version() == (major<<16 | minor<<8 | patch)
    static const int aomVersion_3_14_0 = (3 << 16) | (14 << 8);
    const int aomVersion = aom_codec_version();
    avifBool useAllIntraForLayered = aomVersion < aomVersion_3_14_0 && encoder->extraLayerCount == 1 &&
                                     codec->internal->qualityFirstLayer <= TWO_LAYER_ALL_INTRA_QUALITY_THRESHOLD;
    // Also use all-intra encoding when encoding still images.
    avifBool useAllIntra = (addImageFlags & AVIF_ADD_IMAGE_FLAG_SINGLE) || useAllIntraForLayered;

    // Map encoder speed to AOM usage + CpuUsed:
    // Speed  0: GoodQuality CpuUsed 0
    // Speed  1: GoodQuality CpuUsed 1
    // Speed  2: GoodQuality CpuUsed 2
    // Speed  3: GoodQuality CpuUsed 3
    // Speed  4: GoodQuality CpuUsed 4
    // Speed  5: GoodQuality CpuUsed 5
    // Speed  6: GoodQuality CpuUsed 6
    // Speed  7: RealTime    CpuUsed 7
    // Speed  8: RealTime    CpuUsed 8
    // Speed  9: RealTime    CpuUsed 9
    // Speed 10: RealTime    CpuUsed 9
    unsigned int aomUsage = AOM_USAGE_GOOD_QUALITY;
    // Use AOM_USAGE_ALL_INTRA (added in https://crbug.com/aomedia/2959) if available.
#if defined(AOM_USAGE_ALL_INTRA)
    if (useAllIntra) {
        aomUsage = AOM_USAGE_ALL_INTRA;
    }
#endif