void ff_audio_convert_free(AudioConvert **ac)
{
if (!*ac)
return;
ff_dither_free(&(*ac)->dc);
av_freep(ac);
}
DitherContext *ff_dither_alloc(AVAudioResampleContext *avr,
enum AVSampleFormat out_fmt,
enum AVSampleFormat in_fmt,
int channels, int sample_rate)
{
AVLFG seed_gen;
DitherContext *c;
int ch;
if (av_get_packed_sample_fmt(out_fmt) != AV_SAMPLE_FMT_S16 ||
av_get_bytes_per_sample(in_fmt) <= 2) {
av_log(avr, AV_LOG_ERROR, "dithering %s to %s is not supported\n",
av_get_sample_fmt_name(in_fmt), av_get_sample_fmt_name(out_fmt));
return NULL;
}
c = av_mallocz(sizeof(*c));
if (!c)
return NULL;
if (avr->dither_method == AV_RESAMPLE_DITHER_TRIANGULAR_NS &&
sample_rate != 48000 && sample_rate != 44100) {
av_log(avr, AV_LOG_WARNING, "sample rate must be 48000 or 44100 Hz "
"for triangular_ns dither. using triangular_hp instead.\n");
avr->dither_method = AV_RESAMPLE_DITHER_TRIANGULAR_HP;
}
c->method = avr->dither_method;
dither_init(&c->ddsp, c->method);
if (c->method == AV_RESAMPLE_DITHER_TRIANGULAR_NS) {
if (sample_rate == 48000) {
c->ns_coef_b = ns_48_coef_b;
c->ns_coef_a = ns_48_coef_a;
} else {
c->ns_coef_b = ns_44_coef_b;
c->ns_coef_a = ns_44_coef_a;
}
}
/* Either s16 or s16p output format is allowed, but s16p is used
internally, so we need to use a temp buffer and interleave if the output
format is s16 */
if (out_fmt != AV_SAMPLE_FMT_S16P) {
c->s16_data = ff_audio_data_alloc(channels, 1024, AV_SAMPLE_FMT_S16P,
"dither s16 buffer");
if (!c->s16_data)
goto fail;
c->ac_out = ff_audio_convert_alloc(avr, out_fmt, AV_SAMPLE_FMT_S16P,
channels, sample_rate);
if (!c->ac_out)
goto fail;
}
if (in_fmt != AV_SAMPLE_FMT_FLTP) {
c->flt_data = ff_audio_data_alloc(channels, 1024, AV_SAMPLE_FMT_FLTP,
"dither flt buffer");
if (!c->flt_data)
goto fail;
c->ac_in = ff_audio_convert_alloc(avr, AV_SAMPLE_FMT_FLTP, in_fmt,
channels, sample_rate);
if (!c->ac_in)
goto fail;
}
c->state = av_mallocz(channels * sizeof(*c->state));
if (!c->state)
goto fail;
c->channels = channels;
/* calculate thresholds for turning off dithering during periods of
silence to avoid replacing digital silence with quiet dither noise */
c->mute_dither_threshold = lrintf(sample_rate * MUTE_THRESHOLD_SEC);
c->mute_reset_threshold = c->mute_dither_threshold * 4;
/* initialize dither states */
av_lfg_init(&seed_gen, 0xC0FFEE);
for (ch = 0; ch < channels; ch++) {
DitherState *state = &c->state[ch];
state->mute = c->mute_reset_threshold + 1;
state->seed = av_lfg_get(&seed_gen);
generate_dither_noise(c, state, FFMAX(32768, sample_rate / 2));
}
return c;
fail:
ff_dither_free(&c);
return NULL;
}
