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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This file contains an implementation of a H264BitstreamBuffer class for
// constructing raw bitstream buffers containing NAL units in
// H.264 Annex-B stream format.
// See H.264 spec Annex B and chapter 7for more details.
#include <stddef.h>
#include <stdint.h>
#include "base/gtest_prod_util.h"
#include "base/numerics/safe_conversions.h"
#include "media/base/media_export.h"
#include "media/base/video_frame.h"
#include "media/filters/h264_parser.h"
namespace media {
// Holds one or more NALUs as a raw bitstream buffer in H.264 Annex-B format.
// Note that this class currently does NOT insert emulation prevention
// three-byte sequences (spec 7.3.1).
class MEDIA_EXPORT H264BitstreamBuffer {
// Discard all data and reset the buffer for reuse.
void Reset();
// Append |num_bits| bits to the stream from |val|.
// |val| is interpreted in the host endianness.
template <typename T>
void AppendBits(size_t num_bits, T val) {
AppendU64(num_bits, static_cast<uint64_t>(val));
void AppendBits(size_t num_bits, bool val) {
DCHECK_EQ(num_bits, 1ul);
// Append a one-bit bool/flag value |val| to the stream.
void AppendBool(bool val);
// Append a signed value in |val| in Exp-Golomb code.
void AppendSE(int val);
// Append an unsigned value in |val| in Exp-Golomb code.
void AppendUE(unsigned int val);
// Start a new NALU of type |nalu_type| and with given |nal_ref_idc|
// (see spec). Note, that until FinishNALU() is called, some of the bits
// may not be flushed into the buffer and the data will not be correctly
// aligned with trailing bits.
void BeginNALU(H264NALU::Type nalu_type, int nal_ref_idc);
// Finish current NALU. This will flush any cached bits and correctly align
// the buffer with RBSP trailing bits. This MUST be called for the stream
// returned by data() to be correct.
void FinishNALU();
// Return number of full bytes in the stream. Note that FinishNALU() has to
// be called to flush cached bits, or the return value will not include them.
size_t BytesInBuffer();
// Return a pointer to the stream. FinishNALU() must be called before
// accessing the stream, otherwise some bits may still be cached and not
// in the buffer.
uint8_t* data();
// Allocate additional memory (kGrowBytes bytes) for the buffer.
void Grow();
// Append |num_bits| bits from U64 value |val| (in host endianness).
void AppendU64(size_t num_bits, uint64_t val);
// Flush any cached bits in the reg with byte granularity, i.e. enough
// bytes to flush all pending bits, but not more.
void FlushReg();
typedef uint64_t RegType;
enum {
// Sizes of reg_.
kRegByteSize = sizeof(RegType),
kRegBitSize = kRegByteSize * 8,
// Amount of bytes to grow the buffer by when we run out of
// previously-allocated memory for it.
kGrowBytes = 4096,
static_assert(kGrowBytes >= kRegByteSize,
"kGrowBytes must be larger than kRegByteSize");
// Unused bits left in reg_.
size_t bits_left_in_reg_;
// Cache for appended bits. Bits are flushed to data_ with kRegByteSize
// granularity, i.e. when reg_ becomes full, or when an explicit FlushReg()
// is called.
RegType reg_;
// Current capacity of data_, in bytes.
size_t capacity_;
// Current byte offset in data_ (points to the start of unwritten bits).
size_t pos_;
// Buffer for stream data.
uint8_t* data_;
} // namespace media