AVRational

Rational number calculation. More...

Files
file	rational.h
	Utilties for rational number calculation.

Classes
struct	AVRational
	Rational number (pair of numerator and denominator). More...

Typedefs
typedef struct AVRational	AVRational
	Rational number (pair of numerator and denominator).

Functions
int	av_reduce (int *dst_num, int *dst_den, int64_t num, int64_t den, int64_t max)
	Reduce a fraction. More...
AVRational	av_mul_q (AVRational b, AVRational c) av_const
	Multiply two rationals. More...
AVRational	av_div_q (AVRational b, AVRational c) av_const
	Divide one rational by another. More...
AVRational	av_add_q (AVRational b, AVRational c) av_const
	Add two rationals. More...
AVRational	av_sub_q (AVRational b, AVRational c) av_const
	Subtract one rational from another. More...
AVRational	av_d2q (double d, int max) av_const
	Convert a double precision floating point number to a rational. More...
int	av_nearer_q (AVRational q, AVRational q1, AVRational q2)
	Find which of the two rationals is closer to another rational. More...
int	av_find_nearest_q_idx (AVRational q, const AVRational *q_list)
	Find the value in a list of rationals nearest a given reference rational. More...
uint32_t	av_q2intfloat (AVRational q)
	Convert an AVRational to a IEEE 32-bit float expressed in fixed-point format. More...

Detailed Description

Rational number calculation.

While rational numbers can be expressed as floating-point numbers, the conversion process is a lossy one, so are floating-point operations. On the other hand, the nature of FFmpeg demands highly accurate calculation of timestamps. This set of rational number utilities serves as a generic interface for manipulating rational numbers as pairs of numerators and denominators.

Many of the functions that operate on AVRational's have the suffix _q, in reference to the mathematical symbol "ℚ" (Q) which denotes the set of all rational numbers.

Function Documentation

av_add_q()

AVRational av_add_q	(	AVRational	b,
		AVRational	c
	)		const

Add two rationals.

Parameters

b	First rational
c	Second rational

Returns

b+c

av_d2q()

AVRational av_d2q	(	double	d,
		int	max
	)		const

Convert a double precision floating point number to a rational.

In case of infinity, the returned value is expressed as {1, 0} or {-1, 0} depending on the sign.

Parameters

d	double to convert
max	Maximum allowed numerator and denominator

Returns

d in AVRational form

See also

av_q2d()

av_div_q()

AVRational av_div_q	(	AVRational	b,
		AVRational	c
	)		const

Divide one rational by another.

Parameters

b	First rational
c	Second rational

Returns

b/c

av_find_nearest_q_idx()

int av_find_nearest_q_idx	(	AVRational	q,
		const AVRational *	q_list
	)

Find the value in a list of rationals nearest a given reference rational.

Parameters

q	Reference rational
q_list	Array of rationals terminated by {0, 0}

Returns

Index of the nearest value found in the array

av_mul_q()

AVRational av_mul_q	(	AVRational	b,
		AVRational	c
	)		const

Multiply two rationals.

Parameters

b	First rational
c	Second rational

Returns

b*c

av_nearer_q()

int av_nearer_q	(	AVRational	q,
		AVRational	q1,
		AVRational	q2
	)

Find which of the two rationals is closer to another rational.

Parameters

q	Rational to be compared against
q1,q2	Rationals to be tested

Returns

One of the following values:

• 1 if q1 is nearer to q than q2
• -1 if q2 is nearer to q than q1
• 0 if they have the same distance

av_q2intfloat()

uint32_t av_q2intfloat

(

AVRational

q

)

Convert an AVRational to a IEEE 32-bit float expressed in fixed-point format.

Parameters

q	Rational to be converted

Returns

Equivalent floating-point value, expressed as an unsigned 32-bit integer.

Note

The returned value is platform-indepedant.

av_reduce()

int av_reduce	(	int *	dst_num,
		int *	dst_den,
		int64_t	num,
		int64_t	den,
		int64_t	max
	)

Reduce a fraction.

This is useful for framerate calculations.

Parameters

[out]	dst_num	Destination numerator
[out]	dst_den	Destination denominator
[in]	num	Source numerator
[in]	den	Source denominator
[in]	max	Maximum allowed values for dst_num & dst_den

Returns

1 if the operation is exact, 0 otherwise

av_sub_q()

AVRational av_sub_q	(	AVRational	b,
		AVRational	c
	)		const

Subtract one rational from another.

Parameters

b	First rational
c	Second rational

Returns

b-c