static int synchronize_audio(VideoState *is, short *samples, int samples_size1, double pts) { int n, samples_size; double ref_clock; n = 2 * is->audio_st->codec->channels; samples_size = samples_size1; /* if not master, then we try to remove or add samples to correct the clock */ if (((is->av_sync_type == AV_SYNC_VIDEO_MASTER && is->video_st) || is->av_sync_type == AV_SYNC_EXTERNAL_CLOCK)) { double diff, avg_diff; int wanted_size, min_size, max_size, nb_samples; ref_clock = get_master_clock(is); diff = get_audio_clock(is) - ref_clock; if (diff < AV_NOSYNC_THRESHOLD) { is->audio_diff_cum = diff + is->audio_diff_avg_coef * is->audio_diff_cum; if (is->audio_diff_avg_count < AUDIO_DIFF_AVG_NB) { /* not enough measures to have a correct estimate */ is->audio_diff_avg_count++; } else { /* estimate the A-V difference */ avg_diff = is->audio_diff_cum * (1.0 - is->audio_diff_avg_coef); if (fabs(avg_diff) >= is->audio_diff_threshold) { wanted_size = samples_size + ((int)(diff * is->audio_st->codec->sample_rate) * n); nb_samples = samples_size / n; min_size = ((nb_samples * (100 - SAMPLE_CORRECTION_PERCENT_MAX)) / 100) * n; max_size = ((nb_samples * (100 + SAMPLE_CORRECTION_PERCENT_MAX)) / 100) * n; if (wanted_size < min_size) wanted_size = min_size; else if (wanted_size > max_size) wanted_size = max_size; /* add or remove samples to correction the synchro */ if (wanted_size < samples_size) { /* remove samples */ samples_size = wanted_size; } else if (wanted_size > samples_size) { uint8_t *samples_end, *q; int nb; /* add samples */ nb = (samples_size - wanted_size); samples_end = (uint8_t *)samples + samples_size - n; q = samples_end + n; while (nb > 0) { memcpy(q, samples_end, n); q += n; nb -= n; } samples_size = wanted_size; } } av_dlog(NULL, "diff=%f adiff=%f sample_diff=%d apts=%0.3f vpts=%0.3f %f\n", diff, avg_diff, samples_size - samples_size1, is->audio_clock, is->video_clock, is->audio_diff_threshold); } } else { /* too big difference : may be initial PTS errors, so reset A-V filter */ is->audio_diff_avg_count = 0; is->audio_diff_cum = 0; } } return samples_size; }