int avpriv_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr) { int frame_size_code; memset(hdr, 0, sizeof(*hdr)); hdr->sync_word = get_bits(gbc, 16); if(hdr->sync_word != 0x0B77) return AAC_AC3_PARSE_ERROR_SYNC; /* read ahead to bsid to distinguish between AC-3 and E-AC-3 */ hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F; if(hdr->bitstream_id > 16) return AAC_AC3_PARSE_ERROR_BSID; hdr->num_blocks = 6; /* set default mix levels */ hdr->center_mix_level = 1; // -4.5dB hdr->surround_mix_level = 1; // -6.0dB if(hdr->bitstream_id <= 10) { /* Normal AC-3 */ hdr->crc1 = get_bits(gbc, 16); hdr->sr_code = get_bits(gbc, 2); if(hdr->sr_code == 3) return AAC_AC3_PARSE_ERROR_SAMPLE_RATE; frame_size_code = get_bits(gbc, 6); if(frame_size_code > 37) return AAC_AC3_PARSE_ERROR_FRAME_SIZE; skip_bits(gbc, 5); // skip bsid, already got it hdr->bitstream_mode = get_bits(gbc, 3); hdr->channel_mode = get_bits(gbc, 3); if(hdr->channel_mode == AC3_CHMODE_STEREO) { skip_bits(gbc, 2); // skip dsurmod } else { if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO) hdr->center_mix_level = get_bits(gbc, 2); if(hdr->channel_mode & 4) hdr->surround_mix_level = get_bits(gbc, 2); } hdr->lfe_on = get_bits1(gbc); hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8; hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift; hdr->bit_rate = (ff_ac3_bitrate_tab[frame_size_code>>1] * 1000) >> hdr->sr_shift; hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on; hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2; hdr->frame_type = EAC3_FRAME_TYPE_AC3_CONVERT; //EAC3_FRAME_TYPE_INDEPENDENT; hdr->substreamid = 0; } else { /* Enhanced AC-3 */ hdr->crc1 = 0; hdr->frame_type = get_bits(gbc, 2); if(hdr->frame_type == EAC3_FRAME_TYPE_RESERVED) return AAC_AC3_PARSE_ERROR_FRAME_TYPE; hdr->substreamid = get_bits(gbc, 3); hdr->frame_size = (get_bits(gbc, 11) + 1) << 1; if(hdr->frame_size < AC3_HEADER_SIZE) return AAC_AC3_PARSE_ERROR_FRAME_SIZE; hdr->sr_code = get_bits(gbc, 2); if (hdr->sr_code == 3) { int sr_code2 = get_bits(gbc, 2); if(sr_code2 == 3) return AAC_AC3_PARSE_ERROR_SAMPLE_RATE; hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2; hdr->sr_shift = 1; } else { hdr->num_blocks = eac3_blocks[get_bits(gbc, 2)]; hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code]; hdr->sr_shift = 0; } hdr->channel_mode = get_bits(gbc, 3); hdr->lfe_on = get_bits1(gbc); hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate / (hdr->num_blocks * 256.0)); hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on; } hdr->channel_layout = ff_ac3_channel_layout_tab[hdr->channel_mode]; if (hdr->lfe_on) hdr->channel_layout |= AV_CH_LOW_FREQUENCY; return 0; }
int avpriv_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr) { int frame_size_code; memset(hdr, 0, sizeof(*hdr)); hdr->sync_word = get_bits(gbc, 16); if(hdr->sync_word != 0x0B77) return AAC_AC3_PARSE_ERROR_SYNC;   hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F; if(hdr->bitstream_id > 16) return AAC_AC3_PARSE_ERROR_BSID; hdr->num_blocks = 6;   hdr->center_mix_level = 1;  