media/base/buffers.h

   1 // Copyright (c) 2012 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 // Timestamps are derived directly from the encoded media file and are commonly
   6 // known as the presentation timestamp (PTS).  Durations are a best-guess and
   7 // are usually derived from the sample/frame rate of the media file.
   8 //
   9 // Due to encoding and transmission errors, it is not guaranteed that timestamps
  10 // arrive in a monotonically increasing order nor that the next timestamp will
  11 // be equal to the previous timestamp plus the duration.
  12 //
  13 // In the ideal scenario for a 25fps movie, buffers are timestamped as followed:
  14 //
  15 //               Buffer0      Buffer1      Buffer2      ...      BufferN
  16 // Timestamp:        0us      40000us      80000us      ...   (N*40000)us
  17 // Duration*:    40000us      40000us      40000us      ...       40000us
  18 //
  19 //  *25fps = 0.04s per frame = 40000us per frame
  20
  21 #ifndef MEDIA_BASE_BUFFERS_H_
  22 #define MEDIA_BASE_BUFFERS_H_
  23
  24 #include "base/basictypes.h"
  25 #include "base/memory/ref_counted.h"
  26 #include "base/time/time.h"
  27 #include "media/base/media_export.h"
  28
  29 namespace media {
  30
  31 // TODO(scherkus): Move the contents of this file elsewhere.
  32
  33 // Indicates an invalid or missing timestamp.
  34 MEDIA_EXPORT extern inline base::TimeDelta kNoTimestamp() {
  35   return base::TimeDelta::FromMicroseconds(kint64min);
  36 }
  37
  38 // Represents an infinite stream duration.
  39 MEDIA_EXPORT extern inline base::TimeDelta kInfiniteDuration() {
  40   return base::TimeDelta::FromMicroseconds(kint64max);
  41 }
  42
  43 }  // namespace media
  44
  45 #endif  // MEDIA_BASE_BUFFERS_H_