libavformat/mp3dec.c

   1 /*
   2  * MP3 demuxer
   3  * Copyright (c) 2003 Fabrice Bellard
   4  *
   5  * This file is part of Libav.
   6  *
   7  * Libav is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * Libav is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with Libav; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 #include "libavutil/avstring.h"
  23 #include "libavutil/intreadwrite.h"
  24 #include "libavutil/dict.h"
  25 #include "libavutil/mathematics.h"
  26 #include "avformat.h"
  27 #include "internal.h"
  28 #include "id3v2.h"
  29 #include "id3v1.h"
  30 #include "libavcodec/mpegaudiodecheader.h"
  31
  32 /* mp3 read */
  33
  34 static int mp3_read_probe(AVProbeData *p)
  35 {
  36     int max_frames, first_frames = 0;
  37     int fsize, frames, sample_rate;
  38     uint32_t header;
  39     uint8_t *buf, *buf0, *buf2, *end;
  40     AVCodecContext avctx;
  41
  42     buf0 = p->buf;
  43     end = p->buf + p->buf_size - sizeof(uint32_t);
  44     while(buf0 < end && !*buf0)
  45         buf0++;
  46
  47     max_frames = 0;
  48     buf = buf0;
  49
  50     for(; buf < end; buf= buf2+1) {
  51         buf2 = buf;
  52
  53         for(frames = 0; buf2 < end; frames++) {
  54             header = AV_RB32(buf2);
  55             fsize = avpriv_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
  56             if(fsize < 0)
  57                 break;
  58             buf2 += fsize;
  59         }
  60         max_frames = FFMAX(max_frames, frames);
  61         if(buf == buf0)
  62             first_frames= frames;
  63     }
  64     // keep this in sync with ac3 probe, both need to avoid
  65     // issues with MPEG-files!
  66     if   (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
  67     else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
  68     else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
  69     else if(max_frames>=1) return 1;
  70     else                   return 0;
  71 //mpegps_mp3_unrecognized_format.mpg has max_frames=3
  72 }
  73
  74 /**
  75  * Try to find Xing/Info/VBRI tags and compute duration from info therein
  76  */
  77 static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
  78 {
  79     uint32_t v, spf;
  80     unsigned frames = 0; /* Total number of frames in file */
  81     unsigned size = 0; /* Total number of bytes in the stream */
  82     const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
  83     MPADecodeHeader c;
  84     int vbrtag_size = 0;
  85
  86     v = avio_rb32(s->pb);
  87     if(ff_mpa_check_header(v) < 0)
  88       return -1;
  89
  90     if (avpriv_mpegaudio_decode_header(&c, v) == 0)
  91         vbrtag_size = c.frame_size;
  92     if(c.layer != 3)
  93         return -1;
  94
  95     /* Check for Xing / Info tag */
  96     avio_skip(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1]);
  97     v = avio_rb32(s->pb);
  98     if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) {
  99         v = avio_rb32(s->pb);
 100         if(v & 0x1)
 101             frames = avio_rb32(s->pb);
 102         if(v & 0x2)
 103             size = avio_rb32(s->pb);
 104     }
 105
 106     /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
 107     avio_seek(s->pb, base + 4 + 32, SEEK_SET);
 108     v = avio_rb32(s->pb);
 109     if(v == MKBETAG('V', 'B', 'R', 'I')) {
 110         /* Check tag version */
 111         if(avio_rb16(s->pb) == 1) {
 112             /* skip delay and quality */
 113             avio_skip(s->pb, 4);
 114             frames = avio_rb32(s->pb);
 115             size = avio_rb32(s->pb);
 116         }
 117     }
 118
 119     if(!frames && !size)
 120         return -1;
 121
 122     /* Skip the vbr tag frame */
 123     avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
 124
 125     spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
 126     if(frames)
 127         st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
 128                                     st->time_base);
 129     if(size && frames)
 130         st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
 131
 132     return 0;
 133 }
 134
 135 static int mp3_read_header(AVFormatContext *s)
 136 {
 137     AVStream *st;
 138     int64_t off;
 139
 140     st = avformat_new_stream(s, NULL);
 141     if (!st)
 142         return AVERROR(ENOMEM);
 143
 144     st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
 145     st->codec->codec_id = CODEC_ID_MP3;
 146     st->need_parsing = AVSTREAM_PARSE_FULL;
 147     st->start_time = 0;
 148
 149     // lcm of all mp3 sample rates
 150     avpriv_set_pts_info(st, 64, 1, 14112000);
 151
 152     off = avio_tell(s->pb);
 153
 154     if (!av_dict_get(s->metadata, "", NULL, AV_DICT_IGNORE_SUFFIX))
 155         ff_id3v1_read(s);
 156
 157     if (mp3_parse_vbr_tags(s, st, off) < 0)
 158         avio_seek(s->pb, off, SEEK_SET);
 159
 160     /* the parameters will be extracted from the compressed bitstream */
 161     return 0;
 162 }
 163
 164 #define MP3_PACKET_SIZE 1024
 165
 166 static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
 167 {
 168     int ret, size;
 169     //    AVStream *st = s->streams[0];
 170
 171     size= MP3_PACKET_SIZE;
 172
 173     ret= av_get_packet(s->pb, pkt, size);
 174
 175     pkt->stream_index = 0;
 176     if (ret <= 0) {
 177         return AVERROR(EIO);
 178     }
 179
 180     if (ret > ID3v1_TAG_SIZE &&
 181         memcmp(&pkt->data[ret - ID3v1_TAG_SIZE], "TAG", 3) == 0)
 182         ret -= ID3v1_TAG_SIZE;
 183
 184     /* note: we need to modify the packet size here to handle the last
 185        packet */
 186     pkt->size = ret;
 187     return ret;
 188 }
 189
 190 AVInputFormat ff_mp3_demuxer = {
 191     .name           = "mp3",
 192     .long_name      = NULL_IF_CONFIG_SMALL("MPEG audio layer 2/3"),
 193     .read_probe     = mp3_read_probe,
 194     .read_header    = mp3_read_header,
 195     .read_packet    = mp3_read_packet,
 196     .flags= AVFMT_GENERIC_INDEX,
 197     .extensions = "mp2,mp3,m2a", /* XXX: use probe */
 198 };