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// Copyright (c) 2011 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
#ifndef MEDIA_BASE_BUFFERS_H_
#define MEDIA_BASE_BUFFERS_H_
#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/time.h"
#include "media/base/media_export.h"
namespace media {
// Indicates an invalid or missing timestamp.
MEDIA_EXPORT extern const base::TimeDelta kNoTimestamp;
class MEDIA_EXPORT StreamSample
: public base::RefCountedThreadSafe<StreamSample> {
public:
// 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;
// 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;
}
protected:
friend class base::RefCountedThreadSafe<StreamSample>;
StreamSample();
virtual ~StreamSample();
base::TimeDelta timestamp_;
base::TimeDelta duration_;
private:
DISALLOW_COPY_AND_ASSIGN(StreamSample);
};
class MEDIA_EXPORT Buffer : public StreamSample {
public:
// 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;
protected:
virtual ~Buffer() {}
};
} // namespace media
#endif // MEDIA_BASE_BUFFERS_H_
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