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// Copyright (c) 2010 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.
// Defines various types of timestamped media buffers used for transporting
// data between filters. Every buffer contains a timestamp in microseconds
// describing the relative position of the buffer within the media stream, and
// the duration in microseconds for the length of time the buffer will be
// rendered.
// Timestamps are derived directly from the encoded media file and are commonly
// known as the presentation timestamp (PTS). Durations are a best-guess and
// are usually derived from the sample/frame rate of the media file.
// Due to encoding and transmission errors, it is not guaranteed that timestamps
// arrive in a monotonically increasing order nor that the next timestamp will
// be equal to the previous timestamp plus the duration.
// In the ideal scenario for a 25fps movie, buffers are timestamped as followed:
// Buffer0 Buffer1 Buffer2 ... BufferN
// Timestamp: 0us 40000us 80000us ... (N*40000)us
// Duration*: 40000us 40000us 40000us ... 40000us
// *25fps = 0.04s per frame = 40000us per frame
#include "base/basictypes.h"
#include "base/ref_counted.h"
#include "base/time.h"
namespace media {
class StreamSample : public base::RefCountedThreadSafe<StreamSample> {
// Constant timestamp value to indicate an invalid or missing timestamp.
static const base::TimeDelta kInvalidTimestamp;
// Returns the timestamp of this buffer in microseconds.
base::TimeDelta GetTimestamp() const {
return timestamp_;
// Returns the duration of this buffer in microseconds.
base::TimeDelta GetDuration() const {
return duration_;
// Indicates that the sample is the last one in the stream. This method is
// pure virtual so implementors can decide when to declare end of stream
// depending on specific data.
virtual bool IsEndOfStream() const = 0;
// Indicates that this sample is discontinuous from the previous one, for
// example, following a seek.
bool IsDiscontinuous() const {
return discontinuous_;
// Sets the timestamp of this buffer in microseconds.
void SetTimestamp(const base::TimeDelta& timestamp) {
timestamp_ = timestamp;
// Sets the duration of this buffer in microseconds.
void SetDuration(const base::TimeDelta& duration) {
duration_ = duration;
// Sets the value returned by IsDiscontinuous().
void SetDiscontinuous(bool discontinuous) {
discontinuous_ = discontinuous;
friend class base::RefCountedThreadSafe<StreamSample>;
virtual ~StreamSample();
base::TimeDelta timestamp_;
base::TimeDelta duration_;
bool discontinuous_;
class Buffer : public StreamSample {
// Returns a read only pointer to the buffer data.
virtual const uint8* GetData() const = 0;
// Returns the size of valid data in bytes.
virtual size_t GetDataSize() const = 0;
// If there's no data in this buffer, it represents end of stream.
virtual bool IsEndOfStream() const { return GetData() == NULL; }
virtual ~Buffer() {}
class WritableBuffer : public Buffer {
// Returns a read-write pointer to the buffer data.
virtual uint8* GetWritableData() = 0;
// Updates the size of valid data in bytes, which must be less than or equal
// to GetBufferSize().
virtual void SetDataSize(size_t data_size) = 0;
// Returns the size of the underlying buffer.
virtual size_t GetBufferSize() const = 0;
virtual ~WritableBuffer() {}
} // namespace media