Half length output with libsox for stereo -> mono

[Stephen.Paterson <stephen.paterson@synety.com>]

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Hi all,

I've found a couple of threads relating to this problem but I can't for the life of me get it to work.

The following command line works fine:

sox original.wav -c 1 -r 8000 converted.wav

I can't get it to work with libsox. I've made a tiny modification to example3.c that should do the same but no matter what I try I always end up with a file that is exactly half the length of the one I get from sox (or some crazy audio).
If I leave the output as stereo I get the full length audio but sadly stereo is no use to me.
The 2 threads I've found are [Sox-devel] 'Effects going crazy' - 2012-05-07 and [SoX] 'Channels/remix does not function as documented' - 2011-11-12
Nothing suggested in either seems to work for me. Could someone take a look at the attached code (it's very simple) to see if they can see what I'm doing wrong please? It's driving me crazy! I'm at the point of giving up and just spawning the sox executable from my code but that would make me cry.

The following is the format of my test input file but it needs to work for any wav file:
RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, stereo 24000 Hz

Desired output will always be in the following format regardless of the input format:
RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 8000 Hz

Apologies if this is more appropriate for sox-users. If so, just let me know and I'll post there.

Cheers


Stephen Paterson
Developer   |  SYNETY
www.synety.com<http://www.synety.com/>

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#include <sox.h>
#include <assert.h>

static void output_message(unsigned level, const char *filename, const char *fmt, va_list ap)
{
	char const * const str[] = {"FAIL", "WARN", "INFO", "DBUG"};
	if (sox_globals.verbosity >= level) {
		fprintf(stderr, "%s %s: ", str[level - 1], filename);
		vfprintf(stderr, fmt, ap);
		fprintf(stderr, "\n");
	}
}

int main(int argc, char * argv[])
{
	static sox_format_t * in, * out;
	sox_effects_chain_t * chain;
	sox_effect_t * e;
	char * args[10];

	assert(argc == 2);
	sox_globals.output_message_handler = output_message;
	sox_globals.verbosity = 10;

	assert(sox_init() == SOX_SUCCESS);
	assert(in = sox_open_read(argv[1], NULL, NULL, NULL));
	assert(out= sox_open_write("converted.wav", &in->signal, NULL, "wav", NULL, NULL));

	chain = sox_create_effects_chain(&in->encoding, &out->encoding);

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

	out->signal.precision = 16;
	out->signal.rate = 8000;
	out->signal.channels = 1;

	if (in->signal.rate != out->signal.rate) {
		e = sox_create_effect(sox_find_effect("rate"));
		assert(sox_effect_options(e, 0, NULL) == SOX_SUCCESS);
		assert(sox_add_effect(chain, e, &in->signal, &out->signal) == SOX_SUCCESS);
		free(e);
	}

	if (in->signal.channels != out->signal.channels) {
		e = sox_create_effect(sox_find_effect("channels"));
		assert(sox_effect_options(e, 0, NULL) == SOX_SUCCESS);
		assert(sox_add_effect(chain, e, &in->signal, &out->signal) == SOX_SUCCESS);
		free(e);
	}

	e = sox_create_effect(sox_find_effect("output"));
	args[0] = (char *)out, assert(sox_effect_options(e, 1, args) == SOX_SUCCESS);
	assert(sox_add_effect(chain, e, &in->signal, &out->signal) == SOX_SUCCESS);
	free(e);

	sox_flow_effects(chain, NULL, NULL);

	sox_delete_effects_chain(chain);
	sox_close(out);
	sox_close(in);
	sox_quit();

	return 0;
}


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