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LibVideo/VP9: Pre-calculate the quantizers at the start of each frame

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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 2023-04-17 00:27:13 -05:00 • committed by Tim Flynn
parent 094b0d8a78
commit 90c0e1ad8f
6 changed files with 104 additions and 70 deletions
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95
Userland/Libraries/LibVideo/VP9/Parser.cpp
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@ -143,6 +143,39 @@ DecoderErrorOr<VideoFullRangeFlag> Parser::read_video_full_range_flag(BigEndianI
return VideoFullRangeFlag::Studio;
}
template<Signed T = i8>
static ErrorOr<T> read_signed(BigEndianInputBitStream& bit_stream, u8 bits)
{
auto value_unsigned = static_cast<T>(TRY(bit_stream.read_bits(bits)));
if (TRY(bit_stream.read_bit()))
return -value_unsigned;
return value_unsigned;
}
static DecoderErrorOr<i8> read_delta_q(BigEndianInputBitStream& bit_stream)
{
if (TRY_READ(bit_stream.read_bit()))
return TRY_READ(read_signed(bit_stream, 4));
return 0;
}
struct QuantizationParameters {
u8 base_quantizer_index { 0 };
i8 y_dc_quantizer_index_delta { 0 };
i8 uv_dc_quantizer_index_delta { 0 };
i8 uv_ac_quantizer_index_delta { 0 };
};
static DecoderErrorOr<QuantizationParameters> quantization_params(BigEndianInputBitStream& bit_stream)
{
QuantizationParameters result;
result.base_quantizer_index = TRY_READ(bit_stream.read_bits(8));
result.y_dc_quantizer_index_delta = TRY(read_delta_q(bit_stream));
result.uv_dc_quantizer_index_delta = TRY(read_delta_q(bit_stream));
result.uv_ac_quantizer_index_delta = TRY(read_delta_q(bit_stream));
return result;
}
/* (6.2) */
DecoderErrorOr<void> Parser::uncompressed_header(FrameContext& frame_context)
{
@ -266,8 +299,10 @@ DecoderErrorOr<void> Parser::uncompressed_header(FrameContext& frame_context)
frame_context.probability_context_index = probability_context_index;
TRY(loop_filter_params(frame_context));
TRY(quantization_params(frame_context));
auto quantization_parameters = TRY(quantization_params(frame_context.bit_stream));
TRY(segmentation_params(frame_context));
precalculate_quantizers(frame_context, quantization_parameters);
TRY(parse_tile_counts(frame_context));
frame_context.header_size_in_bytes = TRY_READ(frame_context.bit_stream.read_bits(16));
@ -399,15 +434,6 @@ DecoderErrorOr<InterpolationFilter> Parser::read_interpolation_filter(BigEndianI
return literal_to_type[TRY_READ(bit_stream.read_bits(2))];
}
template<Signed T = i8>
static ErrorOr<T> read_signed(BigEndianInputBitStream& bit_stream, u8 bits)
{
auto value_unsigned = static_cast<T>(TRY(bit_stream.read_bits(bits)));
if (TRY(bit_stream.read_bit()))
return -value_unsigned;
return value_unsigned;
}
DecoderErrorOr<void> Parser::loop_filter_params(FrameContext& frame_context)
{
// FIXME: These should be moved to their own struct to return here.
@ -433,22 +459,6 @@ DecoderErrorOr<void> Parser::loop_filter_params(FrameContext& frame_context)
return {};
}
DecoderErrorOr<void> Parser::quantization_params(FrameContext& frame_context)
{
frame_context.base_quantizer_index = TRY_READ(frame_context.bit_stream.read_bits(8));
frame_context.y_dc_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
frame_context.uv_dc_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
frame_context.uv_ac_quantizer_index_delta = TRY(read_delta_q(frame_context.bit_stream));
return {};
}
DecoderErrorOr<i8> Parser::read_delta_q(BigEndianInputBitStream& bit_stream)
{
if (TRY_READ(bit_stream.read_bit()))
return TRY_READ(read_signed(bit_stream, 4));
return 0;
}
DecoderErrorOr<void> Parser::segmentation_params(FrameContext& frame_context)
{
frame_context.segmentation_enabled = TRY_READ(frame_context.bit_stream.read_bit());
@ -501,6 +511,35 @@ DecoderErrorOr<u8> Parser::read_prob(BigEndianInputBitStream& bit_stream)
return 255;
}
void Parser::precalculate_quantizers(FrameContext& frame_context, QuantizationParameters quantization_parameters)
{
frame_context.lossless = quantization_parameters.base_quantizer_index == 0
&& quantization_parameters.y_dc_quantizer_index_delta == 0
&& quantization_parameters.uv_dc_quantizer_index_delta == 0
&& quantization_parameters.uv_ac_quantizer_index_delta == 0;
// Pre-calculate the quantizers so that the decoder doesn't have to do it repeatedly.
for (u8 segment_id = 0; segment_id < MAX_SEGMENTS; segment_id++) {
auto alternative_quantizer_feature = frame_context.get_segment_feature(segment_id, SegmentFeature::AlternativeQuantizerBase);
auto base = Decoder::get_base_quantizer_index(alternative_quantizer_feature, frame_context.should_use_absolute_segment_base_quantizer, quantization_parameters.base_quantizer_index);
// The function get_ac_quant( plane ) returns the quantizer value for the ac coefficient for a particular plane and
// is derived as follows:
// − If plane is equal to 0, return ac_q( get_qindex( ) ).
// − Otherwise, return ac_q( get_qindex( ) + delta_q_uv_ac ).
auto& current_quantizers = frame_context.segment_quantizers[segment_id];
current_quantizers.y_ac_quantizer = Decoder::get_ac_quantizer(frame_context.color_config.bit_depth, base, 0);
current_quantizers.uv_ac_quantizer = Decoder::get_ac_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.uv_ac_quantizer_index_delta);
// The function get_dc_quant( plane ) returns the quantizer value for the dc coefficient for a particular plane and
// is derived as follows:
// − If plane is equal to 0, return dc_q( get_qindex( ) + delta_q_y_dc ).
// − Otherwise, return dc_q( get_qindex( ) + delta_q_uv_dc ).
current_quantizers.y_dc_quantizer = Decoder::get_dc_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.y_dc_quantizer_index_delta);
current_quantizers.uv_dc_quantizer = Decoder::get_dc_quantizer(frame_context.color_config.bit_depth, base, quantization_parameters.uv_dc_quantizer_index_delta);
}
}
static u16 calc_min_log2_of_tile_columns(u32 superblock_columns)
{
auto min_log_2 = 0u;
@ -577,7 +616,7 @@ DecoderErrorOr<void> Parser::compressed_header(FrameContext& frame_context)
DecoderErrorOr<TransformMode> Parser::read_tx_mode(BooleanDecoder& decoder, FrameContext const& frame_context)
{
if (frame_context.is_lossless()) {
if (frame_context.lossless) {
return TransformMode::Only_4x4;
}
@ -1373,7 +1412,7 @@ static TransformSet select_transform_type(BlockContext const& block_context, u8
if (plane > 0 || transform_size == Transform_32x32)
return TransformSet { TransformType::DCT, TransformType::DCT };
if (transform_size == Transform_4x4) {
if (block_context.frame_context.is_lossless() || block_context.is_inter_predicted())
if (block_context.frame_context.lossless || block_context.is_inter_predicted())
return TransformSet { TransformType::DCT, TransformType::DCT };
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())];