How to convert loop information between samples and seconds

[uyjulian]

Ren'Py has a feature to loop audio files.

The path and loop information can be passed in like the following syntax:

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<loop 1.2345678>path/to/file.ogg

or

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<from 0.1234567 loop 1.2345678>path/to/file.ogg

The argument to "from" and "loop" are specified in seconds.

However, sometimes, you are using a program that will output the loop arguments in samples, such as Loop Tuner 2.

For example, a file with 1.2345678 seconds of audio that has a sample rate of 44100 has 54444 samples.

You will need the sample rate of the file in order to convert between seconds and samples.
In order to get the sample rate of the file, you can use ffprobe (a command line tool included with ffmpeg) to retrieve information:

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$ ffprobe -show_streams path/to/file.ogg
...
sample_rate=44100
...
duration_ts=54444
duration=1.2345678

sample_rate is the sample rate.
duration_ts is the length of the file in samples.
duration is the length of the file in seconds.

You can use an equation to solve for the number of seconds or the number of seconds.
Let s = number of seconds, a = number of samples, r = sample rate.

The equation is the following:
s = a / r

We can solve for the position in seconds:
s = 54444 / 44100
s = 1.2345578231
54444 samples is equal to 1.2345578231 seconds.

We can solve for the position in samples:
1.2345578231 = a / 44100
Multiply both sides by 44100.
54443.99999871 = a
1.2345578231 seconds is equal to 54443.99999871 samples.

Ren'Py will round towards zero internally when converting between samples and seconds, so it is advised to pass in the precise numbers as arguments.