libavcodec/ac3_parser.c

   1 /*
   2  * AC3 parser
   3  * Copyright (c) 2003 Fabrice Bellard.
   4  * Copyright (c) 2003 Michael Niedermayer.
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #include "parser.h"
  24 #include "ac3_parser.h"
  25 #include "aac_ac3_parser.h"
  26 #include "bitstream.h"
  27
  28
  29 #define AC3_HEADER_SIZE 7
  30
  31
  32 static const uint8_t eac3_blocks[4] = {
  33     1, 2, 3, 6
  34 };
  35
  36 /**
  37  * Table for center mix levels
  38  * reference: Section 5.4.2.4 cmixlev
  39  */
  40 static const uint8_t center_levels[4] = { 2, 3, 4, 3 };
  41
  42 /**
  43  * Table for surround mix levels
  44  * reference: Section 5.4.2.5 surmixlev
  45  */
  46 static const uint8_t surround_levels[4] = { 2, 4, 0, 4 };
  47
  48
  49 int ff_ac3_parse_header(GetBitContext *gbc, AC3HeaderInfo *hdr)
  50 {
  51     int frame_size_code;
  52     int num_blocks;
  53
  54     memset(hdr, 0, sizeof(*hdr));
  55
  56     hdr->sync_word = get_bits(gbc, 16);
  57     if(hdr->sync_word != 0x0B77)
  58         return AC3_PARSE_ERROR_SYNC;
  59
  60     /* read ahead to bsid to distinguish between AC-3 and E-AC-3 */
  61     hdr->bitstream_id = show_bits_long(gbc, 29) & 0x1F;
  62     if(hdr->bitstream_id > 16)
  63         return AC3_PARSE_ERROR_BSID;
  64
  65     if(hdr->bitstream_id <= 10) {
  66         /* Normal AC-3 */
  67         hdr->crc1 = get_bits(gbc, 16);
  68         hdr->sr_code = get_bits(gbc, 2);
  69         if(hdr->sr_code == 3)
  70             return AC3_PARSE_ERROR_SAMPLE_RATE;
  71
  72         frame_size_code = get_bits(gbc, 6);
  73         if(frame_size_code > 37)
  74             return AC3_PARSE_ERROR_FRAME_SIZE;
  75
  76         skip_bits(gbc, 5); // skip bsid, already got it
  77
  78         skip_bits(gbc, 3); // skip bitstream mode
  79         hdr->channel_mode = get_bits(gbc, 3);
  80
  81         /* set default mix levels */
  82         hdr->center_mix_level   = 3;  // -4.5dB
  83         hdr->surround_mix_level = 4;  // -6.0dB
  84
  85         if(hdr->channel_mode == AC3_CHMODE_STEREO) {
  86             skip_bits(gbc, 2); // skip dsurmod
  87         } else {
  88             if((hdr->channel_mode & 1) && hdr->channel_mode != AC3_CHMODE_MONO)
  89                 hdr->center_mix_level = center_levels[get_bits(gbc, 2)];
  90             if(hdr->channel_mode & 4)
  91                 hdr->surround_mix_level = surround_levels[get_bits(gbc, 2)];
  92         }
  93         hdr->lfe_on = get_bits1(gbc);
  94
  95         hdr->sr_shift = FFMAX(hdr->bitstream_id, 8) - 8;
  96         hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code] >> hdr->sr_shift;
  97         hdr->bit_rate = (ff_ac3_bitrate_tab[frame_size_code>>1] * 1000) >> hdr->sr_shift;
  98         hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
  99         hdr->frame_size = ff_ac3_frame_size_tab[frame_size_code][hdr->sr_code] * 2;
 100         hdr->frame_type = EAC3_FRAME_TYPE_AC3_CONVERT; //EAC3_FRAME_TYPE_INDEPENDENT;
 101     } else {
 102         /* Enhanced AC-3 */
 103         hdr->crc1 = 0;
 104         hdr->frame_type = get_bits(gbc, 2);
 105         if(hdr->frame_type == EAC3_FRAME_TYPE_RESERVED)
 106             return AC3_PARSE_ERROR_FRAME_TYPE;
 107
 108         skip_bits(gbc, 3); // skip substream id
 109
 110         hdr->frame_size = (get_bits(gbc, 11) + 1) << 1;
 111         if(hdr->frame_size < AC3_HEADER_SIZE)
 112             return AC3_PARSE_ERROR_FRAME_SIZE;
 113
 114         hdr->sr_code = get_bits(gbc, 2);
 115         if (hdr->sr_code == 3) {
 116             int sr_code2 = get_bits(gbc, 2);
 117             if(sr_code2 == 3)
 118                 return AC3_PARSE_ERROR_SAMPLE_RATE;
 119             hdr->sample_rate = ff_ac3_sample_rate_tab[sr_code2] / 2;
 120             hdr->sr_shift = 1;
 121             num_blocks = 6;
 122         } else {
 123             num_blocks = eac3_blocks[get_bits(gbc, 2)];
 124             hdr->sample_rate = ff_ac3_sample_rate_tab[hdr->sr_code];
 125             hdr->sr_shift = 0;
 126         }
 127
 128         hdr->channel_mode = get_bits(gbc, 3);
 129         hdr->lfe_on = get_bits1(gbc);
 130
 131         hdr->bit_rate = (uint32_t)(8.0 * hdr->frame_size * hdr->sample_rate /
 132                         (num_blocks * 256.0));
 133         hdr->channels = ff_ac3_channels_tab[hdr->channel_mode] + hdr->lfe_on;
 134     }
 135
 136     return 0;
 137 }
 138
 139 int ff_ac3_parse_header_full(GetBitContext *gbc, AC3HeaderInfo *hdr){
 140     int ret, i;
 141     ret = ff_ac3_parse_header(gbc, hdr);
 142     if(!ret){
 143         if(hdr->bitstream_id>10){
 144             /* Enhanced AC-3 */
 145             skip_bits(gbc, 5); // skip bitstream id
 146
 147             /* skip dialog normalization and compression gain */
 148             for (i = 0; i < (hdr->channel_mode ? 1 : 2); i++) {
 149                 skip_bits(gbc, 5); // skip dialog normalization
 150                 if (get_bits1(gbc)) {
 151                     skip_bits(gbc, 8); //skip Compression gain word
 152                 }
 153             }
 154             /* dependent stream channel map */
 155             if (hdr->frame_type == EAC3_FRAME_TYPE_DEPENDENT && get_bits1(gbc)) {
 156                     hdr->channel_map = get_bits(gbc, 16); //custom channel map
 157                     return 0;
 158             }
 159         }
 160         //default channel map based on acmod and lfeon
 161         hdr->channel_map = ff_eac3_default_chmap[hdr->channel_mode];
 162         if(hdr->lfe_on)
 163             hdr->channel_map |= AC3_CHMAP_LFE;
 164     }
 165     return ret;
 166 }
 167
 168 static int ac3_sync(uint64_t state, AACAC3ParseContext *hdr_info,
 169         int *need_next_header, int *new_frame_start)
 170 {
 171     int err;
 172     uint64_t tmp = be2me_64(state);
 173     AC3HeaderInfo hdr;
 174     GetBitContext gbc;
 175
 176     init_get_bits(&gbc, ((uint8_t *)&tmp)+8-AC3_HEADER_SIZE, 54);
 177     err = ff_ac3_parse_header(&gbc, &hdr);
 178
 179     if(err < 0)
 180         return 0;
 181
 182     hdr_info->sample_rate = hdr.sample_rate;
 183     hdr_info->bit_rate = hdr.bit_rate;
 184     hdr_info->channels = hdr.channels;
 185     hdr_info->samples = AC3_FRAME_SIZE;
 186
 187     *need_next_header = (hdr.frame_type != EAC3_FRAME_TYPE_AC3_CONVERT);
 188     *new_frame_start  = (hdr.frame_type != EAC3_FRAME_TYPE_DEPENDENT);
 189     return hdr.frame_size;
 190 }
 191
 192 static av_cold int ac3_parse_init(AVCodecParserContext *s1)
 193 {
 194     AACAC3ParseContext *s = s1->priv_data;
 195     s->header_size = AC3_HEADER_SIZE;
 196     s->sync = ac3_sync;
 197     return 0;
 198 }
 199
 200
 201 AVCodecParser ac3_parser = {
 202     { CODEC_ID_AC3 },
 203     sizeof(AACAC3ParseContext),
 204     ac3_parse_init,
 205     ff_aac_ac3_parse,
 206     NULL,
 207 };