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      1 // Copyright 2014 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 //
      5 // This file contains an implementation of a H264BitstreamBuffer class for
      6 // constructing raw bitstream buffers containing NAL units in
      7 // H.264 Annex-B stream format.
      8 // See H.264 spec Annex B and chapter 7for more details.
      9 
     10 #ifndef MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_
     11 #define MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_
     12 
     13 #include "base/gtest_prod_util.h"
     14 #include "base/numerics/safe_conversions.h"
     15 #include "media/base/media_export.h"
     16 #include "media/base/video_frame.h"
     17 #include "media/filters/h264_parser.h"
     18 
     19 namespace media {
     20 
     21 // Holds one or more NALUs as a raw bitstream buffer in H.264 Annex-B format.
     22 // Note that this class currently does NOT insert emulation prevention
     23 // three-byte sequences (spec 7.3.1).
     24 class MEDIA_EXPORT H264BitstreamBuffer {
     25  public:
     26   H264BitstreamBuffer();
     27   ~H264BitstreamBuffer();
     28 
     29   // Discard all data and reset the buffer for reuse.
     30   void Reset();
     31 
     32   // Append |num_bits| bits to the stream from |val|.
     33   // |val| is interpreted in the host endianness.
     34   template <typename T>
     35   void AppendBits(size_t num_bits, T val) {
     36     AppendU64(num_bits, static_cast<uint64>(val));
     37   }
     38 
     39   void AppendBits(size_t num_bits, bool val) {
     40     DCHECK_EQ(num_bits, 1ul);
     41     AppendBool(val);
     42   }
     43 
     44   // Append a one-bit bool/flag value |val| to the stream.
     45   void AppendBool(bool val);
     46 
     47   // Append a signed value in |val| in Exp-Golomb code.
     48   void AppendSE(int val);
     49 
     50   // Append an unsigned value in |val| in Exp-Golomb code.
     51   void AppendUE(unsigned int val);
     52 
     53   // Start a new NALU of type |nalu_type| and with given |nal_ref_idc|
     54   // (see spec). Note, that until FinishNALU() is called, some of the bits
     55   // may not be flushed into the buffer and the data will not be correctly
     56   // aligned with trailing bits.
     57   void BeginNALU(H264NALU::Type nalu_type, int nal_ref_idc);
     58 
     59   // Finish current NALU. This will flush any cached bits and correctly align
     60   // the buffer with RBSP trailing bits. This MUST be called for the stream
     61   // returned by data() to be correct.
     62   void FinishNALU();
     63 
     64   // Return number of full bytes in the stream. Note that FinishNALU() has to
     65   // be called to flush cached bits, or the return value will not include them.
     66   size_t BytesInBuffer();
     67 
     68   // Return a pointer to the stream. FinishNALU() must be called before
     69   // accessing the stream, otherwise some bits may still be cached and not
     70   // in the buffer.
     71   uint8* data();
     72 
     73  private:
     74   FRIEND_TEST_ALL_PREFIXES(H264BitstreamBufferAppendBitsTest,
     75                            AppendAndVerifyBits);
     76 
     77   // Allocate additional memory (kGrowBytes bytes) for the buffer.
     78   void Grow();
     79 
     80   // Append |num_bits| bits from U64 value |val| (in host endianness).
     81   void AppendU64(size_t num_bits, uint64 val);
     82 
     83   // Flush any cached bits in the reg with byte granularity, i.e. enough
     84   // bytes to flush all pending bits, but not more.
     85   void FlushReg();
     86 
     87   typedef uint64 RegType;
     88   enum {
     89     // Sizes of reg_.
     90     kRegByteSize = sizeof(RegType),
     91     kRegBitSize = kRegByteSize * 8,
     92     // Amount of bytes to grow the buffer by when we run out of
     93     // previously-allocated memory for it.
     94     kGrowBytes = 4096,
     95   };
     96 
     97   COMPILE_ASSERT(kGrowBytes >= kRegByteSize,
     98                  kGrowBytes_must_be_larger_than_kRegByteSize);
     99 
    100   // Unused bits left in reg_.
    101   size_t bits_left_in_reg_;
    102 
    103   // Cache for appended bits. Bits are flushed to data_ with kRegByteSize
    104   // granularity, i.e. when reg_ becomes full, or when an explicit FlushReg()
    105   // is called.
    106   RegType reg_;
    107 
    108   // Current capacity of data_, in bytes.
    109   size_t capacity_;
    110 
    111   // Current byte offset in data_ (points to the start of unwritten bits).
    112   size_t pos_;
    113 
    114   // Buffer for stream data.
    115   uint8* data_;
    116 };
    117 
    118 }  // namespace media
    119 
    120 #endif  // MEDIA_FILTERS_H264_BITSTREAM_BUFFER_H_
    121