How to use soxlib for iOS to remove start and end silence

Question

The task is to remove silence by threshold from the start and end of audio recording. I use this sox port to iOS. https://github.com/shieldlock/SoX-iPhone-Lib/

I've found that command line sox tool makes my task by following command:

sox in.wav out.wav silence 1 0.1 1% reverse silence 1 0.1 1% reverse

(taken from here: http://digitalcardboard.com/blog/2009/08/25/the-sox-of-silence/)

but I cannot to translate it in iOS lib format like this:

sox_create_effect(sox_find_effect("silence"));
args[0] = "2000", assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
assert(sox_add_effect(chain, e, &in->signal, &in->signal) == SOX_SUCCESS);

which parameters I need to give for making this task?

Answer 1

Since sox in.wav out.wav silence 1 0.1 1% reverse silence 1 0.1 1% reverse is a concatenation of two different command lines:

sox in.wav temp.wav silence 1 0.1 1% reverse
sox temp.wav out.wav silence 1 0.1 1% reverse

create two silence effects in your chain. Once effect trims the beginning of the file and pipes a reversed copy to a temp destination, and the next trims from the beginning of the temp and reverses it back to the finished destination.

But what arguments to pass (args)? DISCLAIMER: I have little experience and cannot test this, but I believe it should be these strings:

args[1] = "1";
args[2] = "0.1";
args[3] = "1%";
args[4] = "reverse";

e = sox_create_effect(sox_find_effect("silence"));
args[0] = "2000", assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
assert(sox_add_effect(chain, e, &inFile->signal, &tempFile->signal) == SOX_SUCCESS);
free(e);

e = sox_create_effect(sox_find_effect("silence"));
args[0] = "2000", assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
assert(sox_add_effect(chain, e, &tempFile->signal, &outFile->signal) == SOX_SUCCESS);
free(e);

sox_flow_effects(chain, NULL, NULL);