Mathematics

Mathematical utilities for working with timestamp and time base. More...

Modules
	Colorspace Utility
	AVRational
	Rational number calculation.

Enumerations
enum	AVRounding {   AV_ROUND_ZERO = 0 , AV_ROUND_INF = 1 , AV_ROUND_DOWN = 2 , AV_ROUND_UP = 3 ,   AV_ROUND_NEAR_INF = 5 , AV_ROUND_PASS_MINMAX = 8192 }
	Rounding methods. More...

Functions
int64_t av_const	av_gcd (int64_t a, int64_t b)
	Compute the greatest common divisor of two integer operands. More...
int64_t	av_rescale (int64_t a, int64_t b, int64_t c) av_const
	Rescale a 64-bit integer with rounding to nearest. More...
int64_t	av_rescale_rnd (int64_t a, int64_t b, int64_t c, enum AVRounding rnd) av_const
	Rescale a 64-bit integer with specified rounding. More...
int64_t	av_rescale_q (int64_t a, AVRational bq, AVRational cq) av_const
	Rescale a 64-bit integer by 2 rational numbers. More...
int64_t	av_rescale_q_rnd (int64_t a, AVRational bq, AVRational cq, enum AVRounding rnd) av_const
	Rescale a 64-bit integer by 2 rational numbers with specified rounding. More...
int	av_compare_ts (int64_t ts_a, AVRational tb_a, int64_t ts_b, AVRational tb_b)
	Compare two timestamps each in its own time base. More...
int64_t	av_compare_mod (uint64_t a, uint64_t b, uint64_t mod)
	Compare the remainders of two integer operands divided by a common divisor. More...
int64_t	av_rescale_delta (AVRational in_tb, int64_t in_ts, AVRational fs_tb, int duration, int64_t *last, AVRational out_tb)
	Rescale a timestamp while preserving known durations. More...
int64_t	av_add_stable (AVRational ts_tb, int64_t ts, AVRational inc_tb, int64_t inc)
	Add a value to a timestamp. More...

Detailed Description

Mathematical utilities for working with timestamp and time base.

Enumeration Type Documentation

AVRounding

enum AVRounding

Rounding methods.

Enumerator
AV_ROUND_ZERO	Round toward zero.
AV_ROUND_INF	Round away from zero.
AV_ROUND_DOWN	Round toward -infinity.
AV_ROUND_UP	Round toward +infinity.
AV_ROUND_NEAR_INF	Round to nearest and halfway cases away from zero.
AV_ROUND_PASS_MINMAX	Flag telling rescaling functions to pass INT64_MIN/MAX through unchanged, avoiding special cases for AV_NOPTS_VALUE. Unlike other values of the enumeration AVRounding, this value is a bitmask that must be used in conjunction with another value of the enumeration through a bitwise OR, in order to set behavior for normal cases. av_rescale_rnd(3, 1, 2, AV_ROUND_UP | AV_ROUND_PASS_MINMAX); // Rescaling 3: // Calculating 3 * 1 / 2 // 3 / 2 is rounded up to 2 // => 2 av_rescale_rnd(AV_NOPTS_VALUE, 1, 2, AV_ROUND_UP | AV_ROUND_PASS_MINMAX); // Rescaling AV_NOPTS_VALUE: // AV_NOPTS_VALUE == INT64_MIN // AV_NOPTS_VALUE is passed through // => AV_NOPTS_VALUE

Definition at line 79 of file mathematics.h.

Function Documentation

av_gcd()

int64_t av_const av_gcd	(	int64_t	a,
		int64_t	b
	)

Compute the greatest common divisor of two integer operands.

Parameters

a,b

Operands

Returns

GCD of a and b up to sign; if a >= 0 and b >= 0, return value is >= 0; if a == 0 and b == 0, returns 0.

av_rescale()

int64_t av_rescale	(	int64_t	a,
		int64_t	b,
		int64_t	c
	)		const

Rescale a 64-bit integer with rounding to nearest.

The operation is mathematically equivalent to a * b / c, but writing that directly can overflow.

This function is equivalent to av_rescale_rnd() with AV_ROUND_NEAR_INF.

See also

av_rescale_rnd(), av_rescale_q(), av_rescale_q_rnd()

av_rescale_rnd()

int64_t av_rescale_rnd	(	int64_t	a,
		int64_t	b,
		int64_t	c,
		enum AVRounding	rnd
	)		const

Rescale a 64-bit integer with specified rounding.

The operation is mathematically equivalent to a * b / c, but writing that directly can overflow, and does not support different rounding methods. If the result is not representable then INT64_MIN is returned.

See also

av_rescale(), av_rescale_q(), av_rescale_q_rnd()

Examples

muxing.c, and resampling_audio.c.

Referenced by main(), and write_audio_frame().

av_rescale_q()

int64_t av_rescale_q	(	int64_t	a,
		AVRational	bq,
		AVRational	cq
	)		const

Rescale a 64-bit integer by 2 rational numbers.

The operation is mathematically equivalent to a * bq / cq.

This function is equivalent to av_rescale_q_rnd() with AV_ROUND_NEAR_INF.

See also

av_rescale(), av_rescale_rnd(), av_rescale_q_rnd()

Examples

filtering_video.c, and muxing.c.

Referenced by display_frame(), and write_audio_frame().

av_rescale_q_rnd()

int64_t av_rescale_q_rnd	(	int64_t	a,
		AVRational	bq,
		AVRational	cq,
		enum AVRounding	rnd
	)		const

Rescale a 64-bit integer by 2 rational numbers with specified rounding.

The operation is mathematically equivalent to a * bq / cq.

See also

av_rescale(), av_rescale_rnd(), av_rescale_q()

av_compare_ts()

int av_compare_ts	(	int64_t	ts_a,
		AVRational	tb_a,
		int64_t	ts_b,
		AVRational	tb_b
	)

Compare two timestamps each in its own time base.

Returns

One of the following values:

• -1 if ts_a is before ts_b
• 1 if ts_a is after ts_b
• 0 if they represent the same position

Warning

The result of the function is undefined if one of the timestamps is outside the int64_t range when represented in the other's timebase.

Examples

muxing.c.

Referenced by get_audio_frame(), get_video_frame(), and main().

av_compare_mod()

int64_t av_compare_mod	(	uint64_t	a,
		uint64_t	b,
		uint64_t	mod
	)

Compare the remainders of two integer operands divided by a common divisor.

In other words, compare the least significant log2(mod) bits of integers a and b.

av_compare_mod(0x11, 0x02, 0x10) < 0 // since 0x11 % 0x10  (0x1) < 0x02 % 0x10  (0x2)
av_compare_mod(0x11, 0x02, 0x20) > 0 // since 0x11 % 0x20 (0x11) > 0x02 % 0x20 (0x02)

Parameters

a,b	Operands
mod	Divisor; must be a power of 2

Returns

• a negative value if a % mod < b % mod
• a positive value if a % mod > b % mod
• zero if a % mod == b % mod

av_rescale_delta()

int64_t av_rescale_delta	(	AVRational	in_tb,
		int64_t	in_ts,
		AVRational	fs_tb,
		int	duration,
		int64_t *	last,
		AVRational	out_tb
	)

Rescale a timestamp while preserving known durations.

This function is designed to be called per audio packet to scale the input timestamp to a different time base. Compared to a simple av_rescale_q() call, this function is robust against possible inconsistent frame durations.

The last parameter is a state variable that must be preserved for all subsequent calls for the same stream. For the first call, *last should be initialized to AV_NOPTS_VALUE.

Parameters

[in]	in_tb	Input time base
[in]	in_ts	Input timestamp
[in]	fs_tb	Duration time base; typically this is finer-grained (greater) than in_tb and out_tb
[in]	duration	Duration till the next call to this function (i.e. duration of the current packet/frame)
[in,out]	last	Pointer to a timestamp expressed in terms of fs_tb, acting as a state variable
[in]	out_tb	Output timebase

Returns

Timestamp expressed in terms of out_tb

Note

In the context of this function, "duration" is in term of samples, not seconds.

av_add_stable()

int64_t av_add_stable	(	AVRational	ts_tb,
		int64_t	ts,
		AVRational	inc_tb,
		int64_t	inc
	)

Add a value to a timestamp.

This function guarantees that when the same value is repeatly added that no accumulation of rounding errors occurs.

Parameters

[in]	ts	Input timestamp
[in]	ts_tb	Input timestamp time base
[in]	inc	Value to be added
[in]	inc_tb	Time base of inc