AVRational

Rational number calculation. More...

Files
file	libavutil/rational.h
	Utilities for rational number calculation.

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

Functions
static AVRational	av_make_q (int num, int den)
	Create an AVRational.
static int	av_cmp_q (AVRational a, AVRational b)
	Compare two rationals.
static double	av_q2d (AVRational a)
	Convert an AVRational to a double.
int	av_reduce (int *dst_num, int *dst_den, int64_t num, int64_t den, int64_t max)
	Reduce a fraction.
AVRational	av_mul_q (AVRational b, AVRational c) av_const
	Multiply two rationals.
AVRational	av_div_q (AVRational b, AVRational c) av_const
	Divide one rational by another.
AVRational	av_add_q (AVRational b, AVRational c) av_const
	Add two rationals.
AVRational	av_sub_q (AVRational b, AVRational c) av_const
	Subtract one rational from another.
static av_always_inline AVRational	av_inv_q (AVRational q)
	Invert a rational.
AVRational	av_d2q (double d, int max) av_const
	Convert a double precision floating point number to a rational.
int	av_nearer_q (AVRational q, AVRational q1, AVRational q2)
	Find which of the two rationals is closer to another rational.
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.
uint32_t	av_q2intfloat (AVRational q)
	Convert an AVRational to a IEEE 32-bit float expressed in fixed-point format.
AVRational	av_gcd_q (AVRational a, AVRational b, int max_den, AVRational def)
	Return the best rational so that a and b are multiple of it.

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_make_q()

AVRational av_make_q ( int num, int den )

inlinestatic

Create an AVRational.

Useful for compilers that do not support compound literals.

Note

The return value is not reduced.

See also

av_reduce()

Definition at line 71 of file rational.h.

av_cmp_q()

int av_cmp_q ( AVRational a, AVRational b )

inlinestatic

Compare two rationals.

Parameters

a	First rational
b	Second rational

Returns

One of the following values:

• 0 if a == b
• 1 if a > b
• -1 if a < b
• INT_MIN if one of the values is of the form 0 / 0

Definition at line 89 of file rational.h.

av_q2d()

double av_q2d ( AVRational a )

inlinestatic

Convert an AVRational to a double.

Parameters

a	AVRational to convert

Returns

a in floating-point form

See also

av_d2q()

Definition at line 104 of file rational.h.

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_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_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_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_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

av_inv_q()

av_always_inline AVRational av_inv_q ( AVRational q )

static

Invert a rational.

Parameters

q

value

Returns

1 / q

Examples

qsv_transcode.c, transcode.c, and vaapi_transcode.c.

Definition at line 159 of file rational.h.

Referenced by dec_enc(), dec_enc(), dynamic_set_parameter(), and open_output_file().

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.

In general rational numbers with |num| <= 1<<26 && |den| <= 1<<26 can be recovered exactly from their double representation. (no exceptions were found within 1B random ones)

Parameters

d	double to convert
max	Maximum allowed numerator and denominator

Returns

d in AVRational form

See also

av_q2d()

Examples

qsv_transcode.c.

Referenced by dec_enc(), and dynamic_set_parameter().

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	Rational to be tested
q2	Rational 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_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_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_gcd_q()

AVRational av_gcd_q	(	AVRational	a,
		AVRational	b,
		int	max_den,
		AVRational	def )

Return the best rational so that a and b are multiple of it.

If the resulting denominator is larger than max_den, return def.