-/* header decoding. MUST check the header before because no
- consistency check is done there. Return 1 if free format found and
- that the frame size must be computed externally */
-static int decode_header(MPADecodeContext *s, uint32_t 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);
- sample_rate_index += 3 * (s->lsf + mpeg25);
- s->sample_rate_index = sample_rate_index;
- s->error_protection = ((header >> 16) & 1) ^ 1;
- s->sample_rate = sample_rate;
-
- 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;
- }
- }
-
-#if defined(DEBUG)
- dprintf("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)
- dprintf("ms-");
- if (s->mode_ext & MODE_EXT_I_STEREO)
- dprintf("i-");
- }
- dprintf("stereo");
- } else {
- dprintf("mono");
- }
- dprintf("\n");
-#endif
- return 0;
-}
-
-/* useful helper to get mpeg audio stream infos. Return -1 if error in
- header, otherwise the coded frame size in bytes */
-int mpa_decode_header(AVCodecContext *avctx, uint32_t head)
-{
- MPADecodeContext s1, *s = &s1;
-
- if (ff_mpa_check_header(head) != 0)
- return -1;
-
- if (decode_header(s, head) != 0) {
- return -1;
- }
-
- switch(s->layer) {
- case 1:
- avctx->frame_size = 384;
- break;
- case 2:
- avctx->frame_size = 1152;
- break;
- default:
- case 3:
- if (s->lsf)
- avctx->frame_size = 576;
- else
- avctx->frame_size = 1152;
- break;
- }
-
- avctx->sample_rate = s->sample_rate;
- avctx->channels = s->nb_channels;
- avctx->bit_rate = s->bit_rate;
- avctx->sub_id = s->layer;
- return s->frame_size;
-}
-