Use Tune IQ for layered image inter-frame encoding
Additionally, for avifenc's --progressive: scale the first layer by a
half for further file size savings.
Note: Tune IQ for inter-frame encoding is expected to be available in
libaom v3.14.0.
diff --git a/apps/avifenc.c b/apps/avifenc.c
index b81194b..1c056fe 100644
--- a/apps/avifenc.c
+++ b/apps/avifenc.c
@@ -993,6 +993,10 @@
// reversed lerp, so that last layer reaches exact targetQuality
encoder->quality = targetQuality - (targetQuality - PROGRESSIVE_START_QUALITY) *
(encoder->extraLayerCount - layerIndex) / encoder->extraLayerCount;
+ // We scaled the first layer by a half (numerator: 1, denominator: 2).
+ // Don't perform any scaling for the second layer (numerator: 1, denominator: 1).
+ const avifScalingMode scalingMode = { { 1, 1 }, { 1, 1 } };
+ encoder->scalingMode = scalingMode;
} else {
const avifInputFile * nextFile = avifInputGetFile(input, layerIndex);
// main() function should set number of layers to number of input,
@@ -1160,8 +1164,11 @@
// we should not reach here.
assert(encoder->quality >= PROGRESSIVE_WORST_QUALITY);
// Encode the base layer with a very low quality to ensure a small encoded size.
- encoder->quality = 2;
+ encoder->quality = 10;
// Low alpha quality resulted in weird artifact, so we don't do it.
+ // For further size savings, scale the first layer by a half (numerator: 1, denominator: 2).
+ const avifScalingMode scalingMode = { { 1, 2 }, { 1, 2 } };
+ encoder->scalingMode = scalingMode;
}
if (settings->layers > 1) {
diff --git a/src/codec_aom.c b/src/codec_aom.c
index 10e1bcb..b31509d 100644
--- a/src/codec_aom.c
+++ b/src/codec_aom.c
@@ -664,16 +664,25 @@
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).
+ // 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).
- // 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:
+ // 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)
- // - Option of choosing tune IQ (which requires AOM_USAGE_ALL_INTRA)
- avifBool useAllIntraForLayered = encoder->extraLayerCount == 1 &&
+ // - 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)
+ // TODO(wtc): Update constant with the libaom version that contains the layered-encoding improvements
+ static const int aomVersion_3_14_0 = INT_MAX;
+ 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;
@@ -711,9 +720,7 @@
}
}
- // aom_codec.h says: aom_codec_version() == (major<<16 | minor<<8 | patch)
static const int aomVersion_2_0_0 = (2 << 16);
- const int aomVersion = aom_codec_version();
if (aomVersion <= aomVersion_2_0_0) {
// Issue with v1.0.0-errata1-avif: https://github.com/AOMediaCodec/libavif/issues/56
// Issue with v2.0.0: https://aomedia-review.googlesource.com/q/I26a39791f820b4d4e1d63ff7141f594c3c7181f5
@@ -750,13 +757,18 @@
// AOM_TUNE_IQ has been tuned for the YCbCr family of color spaces, and is favored for
// its low perceptual distortion. AOM_TUNE_IQ partially generalizes to, and benefits
// from other "YUV-like" spaces (e.g. YCgCo and ICtCp) including monochrome (luma only).
- // AOM_TUNE_IQ sets --deltaq-mode=6 which can only be used in all intra mode.
+ //
// AOM_TUNE_IQ was introduced in libaom v3.12.0 but it has significantly different bit
// allocation characteristics compared to v3.13.0. AOM_TUNE_IQ is used by default
// starting with v3.13.0 for fewer behavior changes in libavif.
+ //
+ // Starting with libaom v3.14.0, AOM_TUNE_IQ supports all-intra, good-quality and
+ // realtime modes (for single and layered images). Prior to v3.14.0, AOM_TUNE_IQ is only
+ // supported in all-intra mode.
static const int aomVersion_3_13_0 = (3 << 16) | (13 << 8);
- if (image->matrixCoefficients != AVIF_MATRIX_COEFFICIENTS_IDENTITY && aomUsage == AOM_USAGE_ALL_INTRA &&
- aomVersion >= aomVersion_3_13_0) {
+ if (image->matrixCoefficients != AVIF_MATRIX_COEFFICIENTS_IDENTITY &&
+ ((aomUsage == AOM_USAGE_ALL_INTRA && aomVersion >= aomVersion_3_13_0) ||
+ (encoder->extraLayerCount > 0 && aomVersion >= aomVersion_3_14_0))) {
libavifDefaultTuneMetric = AOM_TUNE_IQ;
}
#endif
@@ -904,6 +916,14 @@
// For layered image, disable lagged encoding to always get output
// frame for each input frame.
cfg->g_lag_in_frames = 0;
+
+ if (aomVersion >= aomVersion_3_14_0) {
+ // Disable QP offsets, so CQ level = frame QP for every frame.
+ // This feature requires libaom 3.14.0 or later.
+ if (cfg->rc_end_usage == AOM_Q) {
+ cfg->use_fixed_qp_offsets = 2;
+ }
+ }
}
if (disableLaggedOutput) {
cfg->g_lag_in_frames = 0;
