mp3dec.c 5.7 KB

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  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. #include "libavutil/avstring.h"
  22. #include "libavutil/intreadwrite.h"
  23. #include "libavutil/dict.h"
  24. #include "libavutil/mathematics.h"
  25. #include "avformat.h"
  26. #include "id3v2.h"
  27. #include "id3v1.h"
  28. #include "libavcodec/mpegaudiodecheader.h"
  29. /* mp3 read */
  30. static int mp3_read_probe(AVProbeData *p)
  31. {
  32. int max_frames, first_frames = 0;
  33. int fsize, frames, sample_rate;
  34. uint32_t header;
  35. uint8_t *buf, *buf0, *buf2, *end;
  36. AVCodecContext avctx;
  37. buf0 = p->buf;
  38. end = p->buf + p->buf_size - sizeof(uint32_t);
  39. while(buf0 < end && !*buf0)
  40. buf0++;
  41. max_frames = 0;
  42. buf = buf0;
  43. for(; buf < end; buf= buf2+1) {
  44. buf2 = buf;
  45. for(frames = 0; buf2 < end; frames++) {
  46. header = AV_RB32(buf2);
  47. fsize = ff_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
  48. if(fsize < 0)
  49. break;
  50. buf2 += fsize;
  51. }
  52. max_frames = FFMAX(max_frames, frames);
  53. if(buf == buf0)
  54. first_frames= frames;
  55. }
  56. // keep this in sync with ac3 probe, both need to avoid
  57. // issues with MPEG-files!
  58. if (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
  59. else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
  60. else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
  61. else if(max_frames>=1) return 1;
  62. else return 0;
  63. //mpegps_mp3_unrecognized_format.mpg has max_frames=3
  64. }
  65. /**
  66. * Try to find Xing/Info/VBRI tags and compute duration from info therein
  67. */
  68. static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
  69. {
  70. uint32_t v, spf;
  71. unsigned frames = 0; /* Total number of frames in file */
  72. unsigned size = 0; /* Total number of bytes in the stream */
  73. const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
  74. MPADecodeHeader c;
  75. int vbrtag_size = 0;
  76. v = avio_rb32(s->pb);
  77. if(ff_mpa_check_header(v) < 0)
  78. return -1;
  79. if (ff_mpegaudio_decode_header(&c, v) == 0)
  80. vbrtag_size = c.frame_size;
  81. if(c.layer != 3)
  82. return -1;
  83. /* Check for Xing / Info tag */
  84. avio_skip(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1]);
  85. v = avio_rb32(s->pb);
  86. if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) {
  87. v = avio_rb32(s->pb);
  88. if(v & 0x1)
  89. frames = avio_rb32(s->pb);
  90. if(v & 0x2)
  91. size = avio_rb32(s->pb);
  92. }
  93. /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
  94. avio_seek(s->pb, base + 4 + 32, SEEK_SET);
  95. v = avio_rb32(s->pb);
  96. if(v == MKBETAG('V', 'B', 'R', 'I')) {
  97. /* Check tag version */
  98. if(avio_rb16(s->pb) == 1) {
  99. /* skip delay and quality */
  100. avio_skip(s->pb, 4);
  101. size = avio_rb32(s->pb);
  102. frames = avio_rb32(s->pb);
  103. }
  104. }
  105. if(!frames && !size)
  106. return -1;
  107. /* Skip the vbr tag frame */
  108. avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
  109. spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
  110. if(frames)
  111. st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
  112. st->time_base);
  113. if(size && frames)
  114. st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
  115. return 0;
  116. }
  117. static int mp3_read_header(AVFormatContext *s,
  118. AVFormatParameters *ap)
  119. {
  120. AVStream *st;
  121. int64_t off;
  122. st = av_new_stream(s, 0);
  123. if (!st)
  124. return AVERROR(ENOMEM);
  125. st->codec->codec_type = AVMEDIA_TYPE_AUDIO;
  126. st->codec->codec_id = CODEC_ID_MP3;
  127. st->need_parsing = AVSTREAM_PARSE_FULL;
  128. st->start_time = 0;
  129. // lcm of all mp3 sample rates
  130. av_set_pts_info(st, 64, 1, 14112000);
  131. off = avio_tell(s->pb);
  132. if (!av_dict_get(s->metadata, "", NULL, AV_DICT_IGNORE_SUFFIX))
  133. ff_id3v1_read(s);
  134. if (mp3_parse_vbr_tags(s, st, off) < 0)
  135. avio_seek(s->pb, off, SEEK_SET);
  136. /* the parameters will be extracted from the compressed bitstream */
  137. return 0;
  138. }
  139. #define MP3_PACKET_SIZE 1024
  140. static int mp3_read_packet(AVFormatContext *s, AVPacket *pkt)
  141. {
  142. int ret, size;
  143. // AVStream *st = s->streams[0];
  144. size= MP3_PACKET_SIZE;
  145. ret= av_get_packet(s->pb, pkt, size);
  146. pkt->stream_index = 0;
  147. if (ret <= 0) {
  148. if(ret<0)
  149. return ret;
  150. return AVERROR_EOF;
  151. }
  152. if (ret > ID3v1_TAG_SIZE &&
  153. memcmp(&pkt->data[ret - ID3v1_TAG_SIZE], "TAG", 3) == 0)
  154. ret -= ID3v1_TAG_SIZE;
  155. /* note: we need to modify the packet size here to handle the last
  156. packet */
  157. pkt->size = ret;
  158. return ret;
  159. }
  160. AVInputFormat ff_mp3_demuxer = {
  161. .name = "mp3",
  162. .long_name = NULL_IF_CONFIG_SMALL("MPEG audio layer 2/3"),
  163. .read_probe = mp3_read_probe,
  164. .read_header = mp3_read_header,
  165. .read_packet = mp3_read_packet,
  166. .flags= AVFMT_GENERIC_INDEX,
  167. .extensions = "mp2,mp3,m2a", /* XXX: use probe */
  168. };