static int decode_header(MPADecodeContext *s, UINT32 header) { int sample_rate, frame_size, mpeg25, padding; int sample_rate_index, bitrate_index; if (header & (1<<20)) { s->lsf = (header & (1<<19)) ? 0 : 1; mpeg25 = 0; } else { s->lsf = 1; mpeg25 = 1; } s->layer = 4 - ((header >> 17) & 3); /* extract frequency */ sample_rate_index = (header >> 10) & 3; sample_rate = mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25); if (sample_rate == 0) return 1; sample_rate_index += 3 * (s->lsf + mpeg25); s->sample_rate_index = sample_rate_index; s->error_protection = ((header >> 16) & 1) ^ 1; bitrate_index = (header >> 12) & 0xf; padding = (header >> 9) & 1; //extension = (header >> 8) & 1; s->mode = (header >> 6) & 3; s->mode_ext = (header >> 4) & 3; //copyright = (header >> 3) & 1; //original = (header >> 2) & 1; //emphasis = header & 3; if (s->mode == MPA_MONO) s->nb_channels = 1; else s->nb_channels = 2; if (bitrate_index != 0) { frame_size = mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index]; s->bit_rate = frame_size * 1000; switch(s->layer) { case 1: frame_size = (frame_size * 12000) / sample_rate; frame_size = (frame_size + padding) * 4; break; case 2: frame_size = (frame_size * 144000) / sample_rate; frame_size += padding; break; default: case 3: frame_size = (frame_size * 144000) / (sample_rate << s->lsf); frame_size += padding; break; } s->frame_size = frame_size; } else { /* if no frame size computed, signal it */ if (!s->free_format_frame_size) return 1; /* free format: compute bitrate and real frame size from the frame size we extracted by reading the bitstream */ s->frame_size = s->free_format_frame_size; switch(s->layer) { case 1: s->frame_size += padding * 4; s->bit_rate = (s->frame_size * sample_rate) / 48000; break; case 2: s->frame_size += padding; s->bit_rate = (s->frame_size * sample_rate) / 144000; break; default: case 3: s->frame_size += padding; s->bit_rate = (s->frame_size * (sample_rate << s->lsf)) / 144000; break; } } s->sample_rate = sample_rate; #if defined(DEBUG) printf("layer%d, %d Hz, %d kbits/s, ", s->layer, s->sample_rate, s->bit_rate); if (s->nb_channels == 2) { if (s->layer == 3) { if (s->mode_ext & MODE_EXT_MS_STEREO) printf("ms-"); if (s->mode_ext & MODE_EXT_I_STEREO) printf("i-"); } printf("stereo"); } else { printf("mono"); } printf("\n"); #endif return 0; }