Quality degradation simulation with OPUS codec.

octopussy.c

#include <stdio.h>
#include <string.h>
#include <math.h>

#include <opus/opus.h>
#include <assert.h>

//#define M_E 2.3504023872876028
#define M_E_1 0.36787944117144233
#define M_E_NEG_M_E_1 2.3504023872876028
#define PI_1 0.3183098861837907
#define T_INCR 0.5

int main()
{
	OpusEncoder* enc;
	OpusDecoder* dec;
	opus_int16 sample_buffer[5760];
	unsigned char opus_buffer[1024];
	size_t num_read;
	opus_int32 opus_buffer_size;
	double t = 0.0;

	enc = opus_encoder_create(48000, 2, OPUS_APPLICATION_AUDIO, NULL);
	dec = opus_decoder_create(48000, 2, NULL);

	assert(opus_encoder_ctl(enc, OPUS_SET_COMPLEXITY(10)) == OPUS_OK);
	assert(opus_encoder_ctl(enc, OPUS_SET_VBR(0)) == OPUS_OK);
	assert(opus_encoder_ctl(enc, OPUS_SET_SIGNAL(OPUS_SIGNAL_MUSIC)) == OPUS_OK);
	assert(opus_encoder_ctl(enc, OPUS_SET_BANDWIDTH(OPUS_BANDWIDTH_FULLBAND)) == OPUS_OK);

	for(;;)
	{
		num_read = fread(sample_buffer, sizeof(opus_int16), 5760, stdin);
		if(num_read == 0)
			break;

		// zero the buffer if not enough samples.
//		size_t n_samples = num_read / sizeof(opus_int16);
//		size_t zero_begin = n_samples * sizeof(opus_int16);

//		memset(sample_buffer + zero_begin, 0, 5760*sizeof(opus_int16) - zero_begin);

		// b = (exp(-cos(1/pi * x)) - e) / (e - exp(-1)) * 9000 + 600
		// double bitrate = ((exp(-cos(PI_1/12.0 * t)) - M_E_1) / M_E_NEG_M_E_1) * 90000.0 + 6000.0;

//		double bitrate = 64000 * 2 * fabs(t/60 - floor(t/60 + .5)) + 6000;
		double bitrate = 48000.0 * -.5 * cos(2.0*M_PI*(1.0/240.0)*t) + 24000.0 + 6000.0;

		opus_encoder_ctl(enc, OPUS_SET_BITRATE((opus_int32)bitrate));
		opus_buffer_size = opus_encode(enc, sample_buffer, 2880, opus_buffer, 1024);
		opus_decode(dec, opus_buffer, opus_buffer_size, sample_buffer, 2880, 0);

		fwrite(sample_buffer, sizeof(opus_int16), 5760, stdout);
		t += T_INCR;
	}
}