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WebP/Lossy: It's 'macroblock', not 'metablock'
Somehow my brain decided to change the name of this concept. Not sure why, the spec consistently uses 'macroblock'. No behavior change.
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2 changed files with 25 additions and 25 deletions
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@ -24,20 +24,20 @@
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// * A tiny bit of uncompressed data, storing image dimensions and the size of the first compressed chunk of data, called the first partition
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// * The first partition, which is a entropy-coded bitstream storing:
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// 1. A fixed-size header.
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// The main piece of data this stores is a probability distribution for how pixel values of each metablock are predicted from previously decoded data.
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// The main piece of data this stores is a probability distribution for how pixel values of each macroblock are predicted from previously decoded data.
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// It also stores how may independent entropy-coded bitstreams are used to store the actual pixel data (for all images I've seen so far, just one).
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// 2. For each metablock, it stores how that metablock's pixel values are predicted from previously decoded data (and some more per-metablock metadata).
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// 2. For each macroblock, it stores how that macroblock's pixel values are predicted from previously decoded data (and some more per-macroblock metadata).
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// There are independent prediction modes for Y, U, V.
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// U and V store a single prediction mode per macroblock.
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// Y can store a single prediction mode per macroblock, or it can store one subblock prediction mode for each of the 4x4 luma subblocks.
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// * One or more additional entropy-coded bitstreams ("partitions") that store the discrete cosine transform ("DCT") coefficients for the actual pixel data for each metablock.
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// Each metablock is subdivided into 4x4 tiles called "subblocks". A 16x16 pixel metablock consists of:
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// 0. If the metablock stores 4x4 luma subblock prediction modes, the 4x4 DC coefficients of each subblock's DCT are stored at the start of the macroblock's data,
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// * One or more additional entropy-coded bitstreams ("partitions") that store the discrete cosine transform ("DCT") coefficients for the actual pixel data for each macroblock.
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// Each macroblock is subdivided into 4x4 tiles called "subblocks". A 16x16 pixel macroblock consists of:
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// 0. If the macroblock stores 4x4 luma subblock prediction modes, the 4x4 DC coefficients of each subblock's DCT are stored at the start of the macroblock's data,
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// as coefficients of an inverse Walsh-Hadamard Transform (WHT).
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// 1. 4x4 luma subblocks
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// 2. 2x2 U chrome subblocks
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// 3. 2x2 U chrome subblocks
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// That is, each metablock stores 24 or 25 sets of coefficients.
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// That is, each macroblock stores 24 or 25 sets of coefficients.
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// Each set of coefficients stores 16 numbers, using a combination of a custom prefix tree and dequantization.
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// The inverse DCT output is added to the output of the prediction.
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@ -138,13 +138,13 @@ enum class SegmentFeatureMode {
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};
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struct Segmentation {
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bool update_metablock_segmentation_map { false };
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bool update_macroblock_segmentation_map { false };
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SegmentFeatureMode segment_feature_mode { SegmentFeatureMode::DeltaValueMode };
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i8 quantizer_update_value[4] {};
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i8 loop_filter_update_value[4] {};
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u8 metablock_segment_tree_probabilities[3] = { 255, 255, 255 };
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u8 macroblock_segment_tree_probabilities[3] = { 255, 255, 255 };
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};
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ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder&);
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@ -197,7 +197,7 @@ struct FrameHeader {
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CoefficientProbabilities coefficient_probabilities;
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bool enable_skipping_of_metablocks_containing_only_zero_coefficients {};
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bool enable_skipping_of_macroblocks_containing_only_zero_coefficients {};
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u8 probability_skip_false;
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};
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@ -239,9 +239,9 @@ ErrorOr<FrameHeader> decode_VP8_frame_header(BooleanDecoder& decoder)
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TRY(decode_VP8_frame_header_coefficient_probabilities(decoder, header.coefficient_probabilities));
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// https://datatracker.ietf.org/doc/html/rfc6386#section-9.11 "Remaining Frame Header Data (Key Frame)"
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header.enable_skipping_of_metablocks_containing_only_zero_coefficients = TRY(L(1));
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dbgln_if(WEBP_DEBUG, "mb_no_skip_coeff {}", header.enable_skipping_of_metablocks_containing_only_zero_coefficients);
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if (header.enable_skipping_of_metablocks_containing_only_zero_coefficients) {
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header.enable_skipping_of_macroblocks_containing_only_zero_coefficients = TRY(L(1));
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dbgln_if(WEBP_DEBUG, "mb_no_skip_coeff {}", header.enable_skipping_of_macroblocks_containing_only_zero_coefficients);
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if (header.enable_skipping_of_macroblocks_containing_only_zero_coefficients) {
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header.probability_skip_false = TRY(L(8));
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dbgln_if(WEBP_DEBUG, "prob_skip_false {}", header.probability_skip_false);
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}
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@ -256,11 +256,11 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
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// Corresponds to "update_segmentation()" in section 19.2 of the spec.
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Segmentation segmentation;
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segmentation.update_metablock_segmentation_map = TRY(L(1));
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segmentation.update_macroblock_segmentation_map = TRY(L(1));
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u8 update_segment_feature_data = TRY(L(1));
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dbgln_if(WEBP_DEBUG, "update_mb_segmentation_map {} update_segment_feature_data {}",
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segmentation.update_metablock_segmentation_map, update_segment_feature_data);
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segmentation.update_macroblock_segmentation_map, update_segment_feature_data);
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if (update_segment_feature_data) {
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segmentation.segment_feature_mode = static_cast<SegmentFeatureMode>(TRY(L(1)));
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@ -286,7 +286,7 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
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}
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}
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if (segmentation.update_metablock_segmentation_map) {
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if (segmentation.update_macroblock_segmentation_map) {
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// This reads mb_segment_tree_probs for https://datatracker.ietf.org/doc/html/rfc6386#section-10.
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for (int i = 0; i < 3; ++i) {
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u8 segment_prob_update = TRY(L(1));
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@ -294,7 +294,7 @@ ErrorOr<Segmentation> decode_VP8_frame_header_segmentation(BooleanDecoder& decod
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if (segment_prob_update) {
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u8 segment_prob = TRY(L(8));
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dbgln_if(WEBP_DEBUG, "segment_prob {}", segment_prob);
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segmentation.metablock_segment_tree_probabilities[i] = segment_prob;
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segmentation.macroblock_segment_tree_probabilities[i] = segment_prob;
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}
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}
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}
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@ -407,8 +407,8 @@ struct MacroblockMetadata {
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// https://datatracker.ietf.org/doc/html/rfc6386#section-11.1 "mb_skip_coeff"
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bool skip_coefficients { false };
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IntraMetablockMode intra_y_mode;
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IntraMetablockMode uv_mode;
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IntraMacroblockMode intra_y_mode;
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IntraMacroblockMode uv_mode;
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IntraBlockMode intra_b_modes[16];
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};
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@ -446,14 +446,14 @@ ErrorOr<Vector<MacroblockMetadata>> decode_VP8_macroblock_metadata(BooleanDecode
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for (int mb_x = 0; mb_x < macroblock_width; ++mb_x) {
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MacroblockMetadata metadata;
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if (header.segmentation.update_metablock_segmentation_map)
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metadata.segment_id = TRY(tree_decode(decoder, METABLOCK_SEGMENT_TREE, header.segmentation.metablock_segment_tree_probabilities));
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if (header.segmentation.update_macroblock_segmentation_map)
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metadata.segment_id = TRY(tree_decode(decoder, MACROBLOCK_SEGMENT_TREE, header.segmentation.macroblock_segment_tree_probabilities));
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if (header.enable_skipping_of_metablocks_containing_only_zero_coefficients)
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if (header.enable_skipping_of_macroblocks_containing_only_zero_coefficients)
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metadata.skip_coefficients = TRY(B(header.probability_skip_false));
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int intra_y_mode = TRY(tree_decode(decoder, KEYFRAME_YMODE_TREE, KEYFRAME_YMODE_PROBABILITIES));
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metadata.intra_y_mode = (IntraMetablockMode)intra_y_mode;
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metadata.intra_y_mode = (IntraMacroblockMode)intra_y_mode;
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// "If the Ymode is B_PRED, it is followed by a (tree-coded) mode for each of the 16 Y subblocks."
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if (intra_y_mode == B_PRED) {
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@ -482,7 +482,7 @@ ErrorOr<Vector<MacroblockMetadata>> decode_VP8_macroblock_metadata(BooleanDecode
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}
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}
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metadata.uv_mode = (IntraMetablockMode)TRY(tree_decode(decoder, UV_MODE_TREE, KEYFRAME_UV_MODE_PROBABILITIES));
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metadata.uv_mode = (IntraMacroblockMode)TRY(tree_decode(decoder, UV_MODE_TREE, KEYFRAME_UV_MODE_PROBABILITIES));
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TRY(macroblock_metadata.try_append(metadata));
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}
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