/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
#ifndef AUDIO_TIMESTAMP_H
#define AUDIO_TIMESTAMP_H
#include "common/scummsys.h"
namespace Audio {
/**
* @defgroup audio_timestamp Timestamp
* @ingroup audio
*
* @brief Timestamp class for specifying points in time and measuring time intervals.
* @{
*/
/**
* When dealing with audio and video decoding, it is often necessary to
* measure the time (intervals) in terms of frames, relative to a fixed
* frame rate (that is, a fixed number of frames per seconds). For
* example, in a typical video there are 24 frames per second, and in a
* typical sound there are 44100 frames (i.e. samples for mono sound
* and pairs of samples for stereo) per second.
*
* At the same time, the system clock provided by ScummVM measures time
* in milliseconds. For syncing purposes and other reasons, it is often
* necessary to convert between and compare time measures given on
* one hand as a frame count, and on the other hand as a number of
* milliseconds.
*
* If handled carelessly, this can introduce rounding errors that
* quickly accumulate, resulting in user-noticeable disturbance, such as
* audio and video running out of sync. For example, a typical approach is to
* measure all time in milliseconds. But with a frame rate of 24 frames
* per second, one frame is 41.66666... milliseconds long. On the other
* hand, if measuring in frames, then a similar rounding issue occurs when
* converting from milliseconds to frames.
*
* One solution is to use floating point arithmetic to compute with
* fractional frames resp. (milli)seconds. This has other undesirable
* side effects. Foremost, some platforms that ScummVM runs on still have
* only limited (and slow) floating point support.
*
* This class provides an alternative solution. It stores time in terms of
* frames, but with a twist: client code can specify arbitrary
* (integral) frame rates but, internally, Timestamp modifies the
* frame rate to be a multiple of 1000. This way, both the number of frames
* (relative to the original frame rate), as well as milliseconds can be
* represented as integers. This change is completely hidden from the
* user, however.
*
* A timestamp can be converted to a frame count or milliseconds at
* virtually no cost. Likewise, it is possible to compute the difference
* between two timestamps in terms of milliseconds or number of frames.
* Timestamps can be easily compared using regular comparison operators,
* resulting in nicely readable code. This is even possible for
* timestamps that are specified using different frame rates.
* Client code can modify timestamps by adding a number of frames
* to it, or adding a number of milliseconds. Adding negative amounts is
* also allowed, and a timestamp can even represent a "negative time",
* which is useful when using the timestamp to store a time interval.
*/
class Timestamp {
public:
/**
* Set up a timestamp with a given time and frame rate.
*
* @param msecs Starting time in milliseconds.
* @param framerate Number of frames per second (must be > 0).
*/
Timestamp(uint msecs = 0, uint framerate = 1);
/**
* Set up a timestamp with the given time, frames, and frame rate.
*
* @param secs Starting time in seconds.
* @param frames Starting frames.
* @param framerate Number of frames per second (must be > 0).
*/
Timestamp(uint secs, uint frames, uint framerate);
/**
* Return a timestamp that represents as closely as possible
* the point in time described by this timestamp, but with
* a different frame rate.
*/
Timestamp convertToFramerate(uint newFramerate) const;
/**
* Check whether two timestamps describe the exact same moment
* in time.
*
* This means that two timestamps can compare as equal
* even if they use different frame rates.
*/
bool operator==(const Timestamp &ts) const;
/**
* Check whether two timestamps describe a different moment in time.
*/
bool operator!=(const Timestamp &ts) const;
/**
* Check whether this timestamp describes an earlier moment in time than another timestamp.
*/
bool operator<(const Timestamp &ts) const;
/**
* Check whether this timestamp describes an earlier or the same moment in time as another timestamp.
*/
bool operator<=(const Timestamp &ts) const;
/**
* Check whether this timestamp describes a later moment in time than another timestamp.
*/
bool operator>(const Timestamp &ts) const;
/**
* Check whether this timestamp describes a later or the same moment in time as another timestamp.
*/
bool operator>=(const Timestamp &ts) const;
/**
* Return a new timestamp that corresponds to the time encoded
* by this timestamp with the given number of frames added.
*
* @param frames Number of frames to add.
*/
Timestamp addFrames(int frames) const;
/**
* Return a new timestamp that corresponds to the time encoded
* by this timestamp with the given number of milliseconds added.
*
* @param msecs Number of milliseconds to add.
*/
Timestamp addMsecs(int msecs) const;
/**
* Return a new timestamp with the negative value of the time encoded
* by this timestamp.
*
* This is a unary minus operation.
*/
Timestamp operator-() const;
/**
* Compute the sum of two timestamps.
*
* This is only allowed if they use the same frame rate.
*/
Timestamp operator+(const Timestamp &ts) const;
/**
* Compute the difference between two timestamps.
*
* This is only allowed if they use the same frame rate.
*/
Timestamp operator-(const Timestamp &ts) const;
/**
* Compute the number of frames between this timestamp and @p ts.
*
* The frames are counted with respect to the frame rate used by this
* timestamp (which may differ from the frame rate used by @p ts).
*/
int frameDiff(const Timestamp &ts) const;
/** Compute the number of milliseconds between this timestamp and @p ts. */
int msecsDiff(const Timestamp &ts) const;
/**
* Return the time in milliseconds described by this timestamp,
* rounded down.
*/
int msecs() const;
/**
* Return the time in seconds described by this timestamp,
* rounded down.
*/
inline int secs() const {
return _secs;
}
/**
* Return the time in frames described by this timestamp.
*/
inline int totalNumberOfFrames() const {
return _numFrames / (int)_framerateFactor + _secs * (int)(_framerate / _framerateFactor);
}
/**
* A timestamp consists of a number of seconds, plus a number
* of frames, the latter describing a fraction of a second.
* This method returns the latter number.
*/
inline int numberOfFrames() const {
return _numFrames / (int)_framerateFactor;
}
/** Return the frame rate used by this timestamp. */
inline uint framerate() const { return _framerate / _framerateFactor; }
protected:
/**
* Compare this timestamp to another one and return
* a value similar to strcmp.
*/
int cmp(const Timestamp &ts) const;
/**
* Normalize this timestamp by making _numFrames non-negative
* and reducing its modulo _framerate.
*/
void normalize();
/**
* Add another timestamp to this one and normalize the result.
*/
void addIntern(const Timestamp &ts);
protected:
/**
* The seconds part of this timestamp.
* The total time in seconds represented by this timestamp can be
* computed as follows:
* @code
* _secs + (double)_numFrames / _framerate
* @endcode
*/
int _secs;
/**
* The number of frames that, together with @c _secs, encode the
* timestamp.
*
* The total number of *internal* frames represented
* by this timestamp can be computed as follows:
* @code
* _numFrames + _secs * _framerate
* @endcode
* To obtain the number of frames with respect to the original
* frame rate, this value must be divided by _framerateFactor.
*
* This is always a value greater than or equal to zero.
* The only reason this is an int and not a uint is to
* allow intermediate negative values.
*/
int _numFrames;
/**
* The internal frame rate, i.e. the number of frames per second.
*
* This is computed as the least common multiple of the frame rate
* specified by the client code, and 1000.
* This ensures that both frames and milliseconds can be stored
* without any rounding losses.
*/
uint _framerate;
/**
* Factor by which the original frame rate specified by the client
* code has been multiplied to obtain the internal _framerate value.
*/
uint _framerateFactor;
};
/** @} */
} // End of namespace Audio
#endif