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LibVideo/VP9: Pre-calculate the quantizers at the start of each frame
Quantizers are a constant for the whole frame, except when segment features override them, in which case they are a constant per segment ID. We take advantage of this by pre-calculating those after reading the quantization parameters and segmentation features for a frame. This results in a small 1.5% improvement (~12.9s -> ~12.7s).
This commit is contained in:
Zaggy1024
Tim Flynn
parent
094b0d8a78
commit
90c0e1ad8f
6 changed files with 104 additions and 70 deletions
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@ -32,6 +32,14 @@ enum class FrameShowMode {
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DoNotShowFrame,
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};
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struct Quantizers {
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u16 y_ac_quantizer { 0 };
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u16 uv_ac_quantizer { 0 };
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u16 y_dc_quantizer { 0 };
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u16 uv_dc_quantizer { 0 };
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};
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struct FrameContext {
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public:
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static ErrorOr<FrameContext> create(ReadonlyBytes data,
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@ -126,15 +134,9 @@ public:
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Array<i8, MAX_REF_FRAMES> loop_filter_reference_deltas;
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Array<i8, 2> loop_filter_mode_deltas;
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u8 base_quantizer_index { 0 };
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i8 y_dc_quantizer_index_delta { 0 };
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i8 uv_dc_quantizer_index_delta { 0 };
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i8 uv_ac_quantizer_index_delta { 0 };
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bool is_lossless() const
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{
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// From quantization_params( ) in the spec.
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return base_quantizer_index == 0 && y_dc_quantizer_index_delta == 0 && uv_dc_quantizer_index_delta == 0 && uv_ac_quantizer_index_delta == 0;
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}
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// Set based on quantization_params( ) in the spec.
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bool lossless { false };
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Array<Quantizers, MAX_SEGMENTS> segment_quantizers;
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bool segmentation_enabled { false };
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// Note: We can use Optional<Array<...>> for these tree probabilities, but unfortunately it seems to have measurable performance overhead.
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@ -1169,18 +1169,17 @@ inline u16 ac_q(u8 bit_depth, u8 b)
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return ac_qlookup[(bit_depth - 8) >> 1][clip_3<u8>(0, 255, b)];
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}
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u8 Decoder::get_base_quantizer_index(BlockContext const& block_context)
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u8 Decoder::get_base_quantizer_index(SegmentFeatureStatus alternative_quantizer_feature, bool should_use_absolute_segment_base_quantizer, u8 base_quantizer_index)
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{
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// The function get_qindex( ) returns the quantizer index for the current block and is specified by the following:
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// − If seg_feature_active( SEG_LVL_ALT_Q ) is equal to 1 the following ordered steps apply:
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auto alternative_quantizer_feature = block_context.get_segment_feature(SegmentFeature::UseAlternativeQuantizerBase);
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if (alternative_quantizer_feature.enabled) {
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// 1. Set the variable data equal to FeatureData[ segment_id ][ SEG_LVL_ALT_Q ].
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auto data = alternative_quantizer_feature.value;
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// 2. If segmentation_abs_or_delta_update is equal to 0, set data equal to base_q_idx + data
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if (!block_context.frame_context.should_use_absolute_segment_base_quantizer) {
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data += block_context.frame_context.base_quantizer_index;
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if (!should_use_absolute_segment_base_quantizer) {
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data += base_quantizer_index;
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}
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// 3. Return Clip3( 0, 255, data ).
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@ -1188,33 +1187,29 @@ u8 Decoder::get_base_quantizer_index(BlockContext const& block_context)
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}
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// − Otherwise, return base_q_idx.
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return block_context.frame_context.base_quantizer_index;
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return base_quantizer_index;
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}
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u16 Decoder::get_dc_quantizer(BlockContext const& block_context, u8 plane)
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u16 Decoder::get_dc_quantizer(u8 bit_depth, u8 base, i8 delta)
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{
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// FIXME: The result of this function can be cached. This does not change per frame.
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// NOTE: Delta is selected by the caller based on whether it is for the Y or UV planes.
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// The function get_dc_quant( plane ) returns the quantizer value for the dc coefficient for a particular plane and
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// is derived as follows:
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// − If plane is equal to 0, return dc_q( get_qindex( ) + delta_q_y_dc ).
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// − Otherwise, return dc_q( get_qindex( ) + delta_q_uv_dc ).
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// Instead of if { return }, select the value to add and return.
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i8 offset = plane == 0 ? block_context.frame_context.y_dc_quantizer_index_delta : block_context.frame_context.uv_dc_quantizer_index_delta;
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return dc_q(block_context.frame_context.color_config.bit_depth, static_cast<u8>(get_base_quantizer_index(block_context) + offset));
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return dc_q(bit_depth, static_cast<u8>(base + delta));
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}
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u16 Decoder::get_ac_quantizer(BlockContext const& block_context, u8 plane)
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u16 Decoder::get_ac_quantizer(u8 bit_depth, u8 base, i8 delta)
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{
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// FIXME: The result of this function can be cached. This does not change per frame.
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// NOTE: Delta is selected by the caller based on whether it is for the Y or UV planes.
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// The function get_ac_quant( plane ) returns the quantizer value for the ac coefficient for a particular plane and
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// is derived as follows:
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// − If plane is equal to 0, return ac_q( get_qindex( ) ).
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// − Otherwise, return ac_q( get_qindex( ) + delta_q_uv_ac ).
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// Instead of if { return }, select the value to add and return.
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i8 offset = plane == 0 ? 0 : block_context.frame_context.uv_ac_quantizer_index_delta;
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return ac_q(block_context.frame_context.color_config.bit_depth, static_cast<u8>(get_base_quantizer_index(block_context) + offset));
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return ac_q(bit_depth, static_cast<u8>(base + delta));
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}
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DecoderErrorOr<void> Decoder::reconstruct(u8 plane, BlockContext const& block_context, u32 transform_block_x, u32 transform_block_y, TransformSize transform_block_size, TransformSet transform_set)
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@ -1254,18 +1249,15 @@ DecoderErrorOr<void> Decoder::reconstruct_templated(u8 plane, BlockContext const
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// 1. Dequant[ i ][ j ] is set equal to ( Tokens[ i * n0 + j ] * get_ac_quant( plane ) ) / dqDenom
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// for i = 0..(n0-1), for j = 0..(n0-1)
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Array<Intermediate, block_size * block_size> dequantized;
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Intermediate ac_quant = get_ac_quantizer(block_context, plane);
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for (auto i = 0u; i < block_size; i++) {
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for (auto j = 0u; j < block_size; j++) {
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auto index = i * block_size + j;
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if (index == 0)
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continue;
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dequantized[index] = (block_context.residual_tokens[index] * ac_quant) / dq_denominator;
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}
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auto quantizers = block_context.frame_context.segment_quantizers[block_context.segment_id];
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Intermediate ac_quant = plane == 0 ? quantizers.y_ac_quantizer : quantizers.uv_ac_quantizer;
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auto const* tokens_raw = block_context.residual_tokens.data();
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for (u32 i = 0; i < dequantized.size(); i++) {
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dequantized[i] = (tokens_raw[i] * ac_quant) / dq_denominator;
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}
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// 2. Dequant[ 0 ][ 0 ] is set equal to ( Tokens[ 0 ] * get_dc_quant( plane ) ) / dqDenom
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dequantized[0] = (block_context.residual_tokens[0] * get_dc_quantizer(block_context, plane)) / dq_denominator;
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dequantized[0] = (block_context.residual_tokens[0] * (plane == 0 ? quantizers.y_dc_quantizer : quantizers.uv_dc_quantizer)) / dq_denominator;
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// It is a requirement of bitstream conformance that the values written into the Dequant array in steps 1 and 2
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// are representable by a signed integer with 8 + BitDepth bits.
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@ -1819,7 +1811,7 @@ DecoderErrorOr<void> Decoder::inverse_transform_2d(BlockContext const& block_con
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// 2. If Lossless is equal to 1, invoke the Inverse WHT process as specified in section 8.7.1.10 with shift equal
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// to 2.
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if (block_context.frame_context.is_lossless()) {
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if (block_context.frame_context.lossless) {
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TRY(inverse_walsh_hadamard_transform(row, log2_of_block_size, 2));
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continue;
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}
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@ -1857,7 +1849,7 @@ DecoderErrorOr<void> Decoder::inverse_transform_2d(BlockContext const& block_con
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// 2. If Lossless is equal to 1, invoke the Inverse WHT process as specified in section 8.7.1.10 with shift equal
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// to 0.
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if (block_context.frame_context.is_lossless()) {
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if (block_context.frame_context.lossless) {
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TRY(inverse_walsh_hadamard_transform(column, log2_of_block_size, 2));
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continue;
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}
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@ -1885,7 +1877,7 @@ DecoderErrorOr<void> Decoder::inverse_transform_2d(BlockContext const& block_con
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// 6. Otherwise (Lossless is equal to 0), set Dequant[ i ][ j ] equal to Round2( T[ i ], Min( 6, n + 2 ) )
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// for i = 0..(n0-1).
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if (!block_context.frame_context.is_lossless()) {
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if (!block_context.frame_context.lossless) {
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for (auto i = 0u; i < block_size; i++) {
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auto index = i * block_size + j;
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dequantized[index] = rounded_right_shift(dequantized[index], min(6, log2_of_block_size + 2));
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@ -73,11 +73,11 @@ private:
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/* (8.6) Reconstruction and Dequantization */
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// Returns the quantizer index for the current block
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static u8 get_base_quantizer_index(BlockContext const&);
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static u8 get_base_quantizer_index(SegmentFeatureStatus alternative_quantizer_feature, bool should_use_absolute_segment_base_quantizer, u8 base_quantizer_index);
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// Returns the quantizer value for the dc coefficient for a particular plane
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static u16 get_dc_quantizer(BlockContext const&, u8 plane);
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static u16 get_dc_quantizer(u8 bit_depth, u8 base, i8 delta);
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// Returns the quantizer value for the ac coefficient for a particular plane
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static u16 get_ac_quantizer(BlockContext const&, u8 plane);
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static u16 get_ac_quantizer(u8 bit_depth, u8 base, i8 delta);
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// (8.6.2) Reconstruct process
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DecoderErrorOr<void> reconstruct(u8 plane, BlockContext const&, u32 transform_block_x, u32 transform_block_y, TransformSize transform_block_size, TransformSet);
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@ -163,9 +163,9 @@ enum Token : u8 {
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enum class SegmentFeature : u8 {
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// SEG_LVL_ALT_Q
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UseAlternativeQuantizerBase,
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AlternativeQuantizerBase,
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// SEG_LVL_ALT_L
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UseAlternativeLoopFilterBase,
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AlternativeLoopFilterBase,
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// SEG_LVL_REF_FRAME
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ReferenceFrameOverride,
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// SEG_LVL_SKIP
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@ -143,6 +143,39 @@ DecoderErrorOr<VideoFullRangeFlag> Parser::read_video_full_range_flag(BigEndianI
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return VideoFullRangeFlag::Studio;
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}
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template<Signed T = i8>
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static ErrorOr<T> read_signed(BigEndianInputBitStream& bit_stream, u8 bits)
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{
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auto value_unsigned = static_cast<T>(TRY(bit_stream.read_bits(bits)));
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if (TRY(bit_stream.read_bit()))
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return -value_unsigned;
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return value_unsigned;
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}
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static DecoderErrorOr<i8> read_delta_q(BigEndianInputBitStream& bit_stream)
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{
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if (TRY_READ(bit_stream.read_bit()))
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return TRY_READ(read_signed(bit_stream, 4));
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return 0;
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}
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struct QuantizationParameters {
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u8 base_quantizer_index { 0 };
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i8 y_dc_quantizer_index_delta { 0 };
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i8 uv_dc_quantizer_index_delta { 0 };
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i8 uv_ac_quantizer_index_delta { 0 };
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};
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static DecoderErrorOr<QuantizationParameters> quantization_params(BigEndianInputBitStream& bit_stream)
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{
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QuantizationParameters result;
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result.base_quantizer_index = TRY_READ(bit_stream.read_bits(8));
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result.y_dc_quantizer_index_delta = TRY(read_delta_q(bit_stream));
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result.uv_dc_quantizer_index_delta = TRY(read_delta_q(bit_stream));
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result.uv_ac_quantizer_index_delta = TRY(read_delta_q(bit_stream));
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return result;
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}
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/* (6.2) */
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DecoderErrorOr<void> Parser::uncompressed_header(FrameContext& frame_context)
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{
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@ -266,8 +299,10 @@ DecoderErrorOr<void> Parser::uncompressed_header(FrameContext& frame_context)
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frame_context.probability_context_index = probability_context_index;
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TRY(loop_filter_params(frame_context));
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TRY(quantization_params(frame_context));
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auto quantization_parameters = TRY(quantization_params(frame_context.bit_stream));
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TRY(segmentation_params(frame_context));
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precalculate_quantizers(frame_context, quantization_parameters);
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TRY(parse_tile_counts(frame_context));
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frame_context.header_size_in_bytes = TRY_READ(frame_context.bit_stream.read_bits(16));
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@ -399,15 +434,6 @@ DecoderErrorOr<InterpolationFilter> Parser::read_interpolation_filter(BigEndianI
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return literal_to_type[TRY_READ(bit_stream.read_bits(2))];
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}
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template<Signed T = i8>
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static ErrorOr<T> read_signed(BigEndianInputBitStream& bit_stream, u8 bits)
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{
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auto value_unsigned = static_cast<T>(TRY(bit_stream.read_bits(bits)));
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if (TRY(bit_stream.read_bit()))
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return -value_unsigned;
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return value_unsigned;
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}
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DecoderErrorOr<void> Parser::loop_filter_params(FrameContext& frame_context)
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{
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// FIXME: These should be moved to their own struct to return here.
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@ -433,22 +459,6 @@ DecoderErrorOr<void> Parser::loop_filter_params(FrameContext& frame_context)
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return {};
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}
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DecoderErrorOr<void> Parser::quantization_params(FrameContext& frame_context)
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{
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frame_context.base_quantizer_index = TRY_READ(frame_context.bit_stream.read_bits(8));
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frame_context.y_dc_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
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frame_context.uv_dc_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
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frame_context.uv_ac_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
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return {};
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}
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DecoderErrorOr<i8> Parser::read_delta_q(BigEndianInputBitStream& bit_stream)
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{
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if (TRY_READ(bit_stream.read_bit()))
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return TRY_READ(read_signed(bit_stream, 4));
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return 0;
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}
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DecoderErrorOr<void> Parser::segmentation_params(FrameContext& frame_context)
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{
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frame_context.segmentation_enabled = TRY_READ(frame_context.bit_stream.read_bit());
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@ -501,6 +511,35 @@ DecoderErrorOr<u8> Parser::read_prob(BigEndianInputBitStream& bit_stream)
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return 255;
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}
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void Parser::precalculate_quantizers(FrameContext& frame_context, QuantizationParameters quantization_parameters)
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{
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frame_context.lossless = quantization_parameters.base_quantizer_index == 0
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&& quantization_parameters.y_dc_quantizer_index_delta == 0
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&& quantization_parameters.uv_dc_quantizer_index_delta == 0
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&& quantization_parameters.uv_ac_quantizer_index_delta == 0;
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// Pre-calculate the quantizers so that the decoder doesn't have to do it repeatedly.
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for (u8 segment_id = 0; segment_id < MAX_SEGMENTS; segment_id++) {
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auto alternative_quantizer_feature = frame_context.get_segment_feature(segment_id, SegmentFeature::AlternativeQuantizerBase);
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auto base = Decoder::get_base_quantizer_index(alternative_quantizer_feature, frame_context.should_use_absolute_segment_base_quantizer, quantization_parameters.base_quantizer_index);
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// The function get_ac_quant( plane ) returns the quantizer value for the ac coefficient for a particular plane and
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// is derived as follows:
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// − If plane is equal to 0, return ac_q( get_qindex( ) ).
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// − Otherwise, return ac_q( get_qindex( ) + delta_q_uv_ac ).
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auto& current_quantizers = frame_context.segment_quantizers[segment_id];
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current_quantizers.y_ac_quantizer = Decoder::get_ac_quantizer(frame_context.color_config.bit_depth, base, 0);
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current_quantizers.uv_ac_quantizer = Decoder::get_ac_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.uv_ac_quantizer_index_delta);
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// The function get_dc_quant( plane ) returns the quantizer value for the dc coefficient for a particular plane and
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// is derived as follows:
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// − If plane is equal to 0, return dc_q( get_qindex( ) + delta_q_y_dc ).
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// − Otherwise, return dc_q( get_qindex( ) + delta_q_uv_dc ).
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current_quantizers.y_dc_quantizer = Decoder::get_dc_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.y_dc_quantizer_index_delta);
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current_quantizers.uv_dc_quantizer = Decoder::get_dc_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.uv_dc_quantizer_index_delta);
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}
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}
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static u16 calc_min_log2_of_tile_columns(u32 superblock_columns)
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{
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auto min_log_2 = 0u;
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@ -577,7 +616,7 @@ DecoderErrorOr<void> Parser::compressed_header(FrameContext& frame_context)
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DecoderErrorOr<TransformMode> Parser::read_tx_mode(BooleanDecoder& decoder, FrameContext const& frame_context)
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{
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if (frame_context.is_lossless()) {
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if (frame_context.lossless) {
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return TransformMode::Only_4x4;
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}
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@ -1373,7 +1412,7 @@ static TransformSet select_transform_type(BlockContext const& block_context, u8
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if (plane > 0 || transform_size == Transform_32x32)
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return TransformSet { TransformType::DCT, TransformType::DCT };
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if (transform_size == Transform_4x4) {
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if (block_context.frame_context.is_lossless() || block_context.is_inter_predicted())
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if (block_context.frame_context.lossless || block_context.is_inter_predicted())
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return TransformSet { TransformType::DCT, TransformType::DCT };
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return mode_to_txfm_map[to_underlying(block_context.size < Block_8x8 ? block_context.sub_block_prediction_modes[block_index] : block_context.y_prediction_mode())];
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@ -30,6 +30,7 @@ struct FrameContext;
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struct TileContext;
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struct BlockContext;
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struct MotionVectorCandidate;
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struct QuantizationParameters;
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class Parser {
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friend class TreeParser;
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@ -61,10 +62,10 @@ private:
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DecoderErrorOr<void> compute_image_size(FrameContext&);
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DecoderErrorOr<InterpolationFilter> read_interpolation_filter(BigEndianInputBitStream&);
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DecoderErrorOr<void> loop_filter_params(FrameContext&);
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DecoderErrorOr<void> quantization_params(FrameContext&);
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DecoderErrorOr<i8> read_delta_q(BigEndianInputBitStream&);
|
||||
DecoderErrorOr<void> segmentation_params(FrameContext&);
|
||||
DecoderErrorOr<u8> read_prob(BigEndianInputBitStream&);
|
||||
static void precalculate_quantizers(FrameContext& frame_context, QuantizationParameters quantization_parameters);
|
||||
DecoderErrorOr<void> parse_tile_counts(FrameContext&);
|
||||
void setup_past_independence();
|
||||
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue