libavformat/mp3dec.c

   1 /*
   2  * MP3 demuxer
   3  * Copyright (c) 2003 Fabrice Bellard
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg 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  * FFmpeg 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 FFmpeg; 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 "avformat.h"
  25 #include "id3v2.h"
  26 #include "id3v1.h"
  27 #include "libavcodec/mpegaudiodecheader.h"
  28
  29 /* mp3 read */
  30
  31 static int mp3_read_probe(AVProbeData *p)
  32 {
  33     int max_frames, first_frames = 0;
  34     int fsize, frames, sample_rate;
  35     uint32_t header;
  36     uint8_t *buf, *buf0, *buf2, *end;
  37     AVCodecContext avctx;
  38
  39     buf0 = p->buf;
  40     end = p->buf + p->buf_size - sizeof(uint32_t);
  41     while(buf0 < end && !*buf0)
  42         buf0++;
  43
  44     max_frames = 0;
  45     buf = buf0;
  46
  47     for(; buf < end; buf= buf2+1) {
  48         buf2 = buf;
  49
  50         for(frames = 0; buf2 < end; frames++) {
  51             header = AV_RB32(buf2);
  52             fsize = ff_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
  53             if(fsize < 0)
  54                 break;
  55             buf2 += fsize;
  56         }
  57         max_frames = FFMAX(max_frames, frames);
  58         if(buf == buf0)
  59             first_frames= frames;
  60     }
  61     // keep this in sync with ac3 probe, both need to avoid
  62     // issues with MPEG-files!
  63     if   (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
  64     else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
  65     else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
  66     else if(max_frames>=1) return 1;
  67     else                   return 0;
  68 //mpegps_mp3_unrecognized_format.mpg has max_frames=3
  69 }
  70
  71 /**
  72  * Try to find Xing/Info/VBRI tags and compute duration from info therein
  73  */
  74 static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
  75 {
  76     uint32_t v, spf;
  77     unsigned frames = 0; /* Total number of frames in file */
  78     unsigned size = 0; /* Total number of bytes in the stream */
  79     const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
  80     MPADecodeHeader c;
  81     int vbrtag_size = 0;
  82
  83     v = get_be32(s->pb);
  84     if(ff_mpa_check_header(v) < 0)
  85       return -1;
  86
  87     if (ff_mpegaudio_decode_header(&c, v) == 0)
  88         vbrtag_size = c.frame_size;
  89     if(c.layer != 3)
  90         return -1;
  91
  92     /* Check for Xing / Info tag */
  93     url_fseek(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1], SEEK_CUR);
  94     v = get_be32(s->pb);
  95     if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) {
  96         v = get_be32(s->pb);
  97         if(v & 0x1)
  98             frames = get_be32(s->pb);
  99         if(v & 0x2)
 100             size = get_be32(s->pb);
 101     }
 102
 103     /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
 104     url_fseek(s->pb, base + 4 + 32, SEEK_SET);
 105     v = get_be32(s->pb);
 106     if(v == MKBETAG('V', 'B', 'R', 'I')) {
 107         /* Check tag version */
 108         if(get_be16(s->pb) == 1) {
 109             /* skip delay and quality */
 110             url_fseek(s->pb, 4, SEEK_CUR);
 111             frames = get_be32(s->pb);
 112             size = get_be32(s->pb);
 113         }
 114     }
 115
 116     if(!frames && !size)
 117         return -1;
 118
 119     /* Skip the vbr tag frame */
 120     url_fseek(s->pb, base + vbrtag_size, SEEK_SET);
 121
 122     spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
 123     if(frames)
 124         st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
 125                                     st->time_base);
 126     if(size && frames)
 127         st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
 128
 129     return 0;
 130 }
 131
 132 static int mp3_read_header(AVFormatContext *s,
 133                            AVFormatParameters *ap)
 134 {
 135     AVStream *st;
 136     int64_t off;
 137
 138     st = av_new_stream(s, 0);
 139     if (!st)
 140         return AVERROR(ENOMEM);
 141
 142     st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
 143     st->codec->codec_id = CODEC_ID_MP3;
 144     st->need_parsing = AVSTREAM_PARSE_FULL;
 145     st->start_time = 0;
 146
 147     // lcm of all mp3 sample rates
 148     av_set_pts_info(st, 64, 1, 14112000);
 149
 150     off = url_ftell(s->pb);
 151
 152     if (!av_metadata_get(s->metadata, "", NULL, AV_METADATA_IGNORE_SUFFIX))
 153         ff_id3v1_read(s);
 154
 155     if (mp3_parse_vbr_tags(s, st, off) < 0)
 156         url_fseek(s->pb, off, SEEK_SET);
 157
 158     /* the parameters will be extracted from the compressed bitstream */
 159     return 0;
 160 }
 161
 162 #define MP3_PACKET_SIZE 1024
 163
 164 static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
 165 {
 166     int ret, size;
 167     //    AVStream *st = s->streams[0];
 168
 169     size= MP3_PACKET_SIZE;
 170
 171     ret= av_get_packet(s->pb, pkt, size);
 172
 173     pkt->stream_index = 0;
 174     if (ret <= 0) {
 175         return AVERROR(EIO);
 176     }
 177     /* note: we need to modify the packet size here to handle the last
 178        packet */
 179     pkt->size = ret;
 180     return ret;
 181 }
 182
 183 AVInputFormat mp3_demuxer = {
 184     "mp3",
 185     NULL_IF_CONFIG_SMALL("MPEG audio layer 2/3"),
 186     0,
 187     mp3_read_probe,
 188     mp3_read_header,
 189     mp3_read_packet,
 190     .flags= AVFMT_GENERIC_INDEX,
 191     .extensions = "mp2,mp3,m2a", /* XXX: use probe */
 192 };