chromium/media/cast/encoding/vpx_quantizer_parser.cc

// Copyright 2015 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/40285824): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif

#include "media/cast/encoding/vpx_quantizer_parser.h"

#include "base/logging.h"
#include "base/memory/raw_ptr.h"

namespace media {
namespace cast {

namespace {
// VpxBitReader is a re-implementation of a subset of the VP8 entropy decoder.
// It is used to decompress the VP8 bitstream for the purposes of quickly
// parsing the VP8 frame headers.  It is mostly the exact same implementation
// found in third_party/libvpx/.../vp8/decoder/dboolhuff.h except that only
// the portion of the implementation needed to parse the frame headers is
// present. As of this writing, the implementation in libvpx could not be
// re-used because of the way that the code is structured, and lack of the
// necessary parts being exported.
class VpxBitReader { … };

// The number of bits to be left-shifted to make the variable range_ over 128.
const uint8_t vpx_shift[128] = …;

// Mapping from the q_index(0-127) to the quantizer value(0-63).
const uint8_t vpx_quantizer_lookup[128] = …;

void VpxBitReader::VpxDecoderReadBytes() { … }

unsigned int VpxBitReader::DecodeBit() { … }

unsigned int VpxBitReader::DecodeValue(unsigned int num_bits) { … }

// Parse the Segment Header part in the first partition.
void ParseSegmentHeader(VpxBitReader* bit_reader) { … }

// Parse the Filter Header in the first partition.
void ParseFilterHeader(VpxBitReader* bit_reader) { … }
}  // unnamed namespace

int ParseVpxHeaderQuantizer(const uint8_t* encoded_data, size_t size) { … }

}  //  namespace cast
}  //  namespace media