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.
5 // This file contains an implementation of an H264 Annex-B video stream parser.
7 #ifndef MEDIA_VIDEO_H264_BIT_READER_H_
8 #define MEDIA_VIDEO_H264_BIT_READER_H_
12 #include <sys/types.h>
14 #include "base/macros.h"
15 #include "media/base/media_export.h"
19 // A class to provide bit-granularity reading of H.264 streams.
20 // This is not a generic bit reader class, as it takes into account
21 // H.264 stream-specific constraints, such as skipping emulation-prevention
22 // bytes and stop bits. See spec for more details.
23 class MEDIA_EXPORT H264BitReader {
28 // Initialize the reader to start reading at |data|, |size| being size
29 // of |data| in bytes.
30 // Return false on insufficient size of stream..
31 // TODO(posciak,fischman): consider replacing Initialize() with
32 // heap-allocating and creating bit readers on demand instead.
33 bool Initialize(const uint8_t* data, off_t size);
35 // Read |num_bits| next bits from stream and return in |*out|, first bit
36 // from the stream starting at |num_bits| position in |*out|.
37 // |num_bits| may be 1-32, inclusive.
38 // Return false if the given number of bits cannot be read (not enough
39 // bits in the stream), true otherwise.
40 bool ReadBits(int num_bits, int* out);
42 // Return the number of bits left in the stream.
45 // See the definition of more_rbsp_data() in spec.
46 bool HasMoreRBSPData();
48 // Return the number of emulation prevention bytes already read.
49 size_t NumEmulationPreventionBytesRead();
52 // Advance to the next byte, loading it into curr_byte_.
53 // Return false on end of stream.
54 bool UpdateCurrByte();
56 // Pointer to the next unread (not in curr_byte_) byte in the stream.
59 // Bytes left in the stream (without the curr_byte_).
62 // Contents of the current byte; first unread bit starting at position
63 // 8 - num_remaining_bits_in_curr_byte_ from MSB.
66 // Number of bits remaining in curr_byte_
67 int num_remaining_bits_in_curr_byte_;
69 // Used in emulation prevention three byte detection (see spec).
70 // Initially set to 0xffff to accept all initial two-byte sequences.
73 // Number of emulation preventation bytes (0x000003) we met.
74 size_t emulation_prevention_bytes_;
76 DISALLOW_COPY_AND_ASSIGN(H264BitReader);
81 #endif // MEDIA_VIDEO_H264_BIT_READER_H_