| 1 | /* |
| 2 | * MPEG Audio header decoder |
| 3 | * Copyright (c) 2001, 2002 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 | /** |
| 23 | * @file |
| 24 | * MPEG Audio header decoder. |
| 25 | */ |
| 26 | |
| 27 | #include "libavutil/common.h" |
| 28 | |
| 29 | #include "avcodec.h" |
| 30 | #include "mpegaudio.h" |
| 31 | #include "mpegaudiodata.h" |
| 32 | #include "mpegaudiodecheader.h" |
| 33 | |
| 34 | |
| 35 | int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header) |
| 36 | { |
| 37 | int sample_rate, frame_size, mpeg25, padding; |
| 38 | int sample_rate_index, bitrate_index; |
| 39 | if (header & (1<<20)) { |
| 40 | s->lsf = (header & (1<<19)) ? 0 : 1; |
| 41 | mpeg25 = 0; |
| 42 | } else { |
| 43 | s->lsf = 1; |
| 44 | mpeg25 = 1; |
| 45 | } |
| 46 | |
| 47 | s->layer = 4 - ((header >> 17) & 3); |
| 48 | /* extract frequency */ |
| 49 | sample_rate_index = (header >> 10) & 3; |
| 50 | if (sample_rate_index >= FF_ARRAY_ELEMS(avpriv_mpa_freq_tab)) |
| 51 | sample_rate_index = 0; |
| 52 | sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25); |
| 53 | sample_rate_index += 3 * (s->lsf + mpeg25); |
| 54 | s->sample_rate_index = sample_rate_index; |
| 55 | s->error_protection = ((header >> 16) & 1) ^ 1; |
| 56 | s->sample_rate = sample_rate; |
| 57 | |
| 58 | bitrate_index = (header >> 12) & 0xf; |
| 59 | padding = (header >> 9) & 1; |
| 60 | //extension = (header >> 8) & 1; |
| 61 | s->mode = (header >> 6) & 3; |
| 62 | s->mode_ext = (header >> 4) & 3; |
| 63 | //copyright = (header >> 3) & 1; |
| 64 | //original = (header >> 2) & 1; |
| 65 | //emphasis = header & 3; |
| 66 | |
| 67 | if (s->mode == MPA_MONO) |
| 68 | s->nb_channels = 1; |
| 69 | else |
| 70 | s->nb_channels = 2; |
| 71 | |
| 72 | if (bitrate_index != 0) { |
| 73 | frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index]; |
| 74 | s->bit_rate = frame_size * 1000; |
| 75 | switch(s->layer) { |
| 76 | case 1: |
| 77 | frame_size = (frame_size * 12000) / sample_rate; |
| 78 | frame_size = (frame_size + padding) * 4; |
| 79 | break; |
| 80 | case 2: |
| 81 | frame_size = (frame_size * 144000) / sample_rate; |
| 82 | frame_size += padding; |
| 83 | break; |
| 84 | default: |
| 85 | case 3: |
| 86 | frame_size = (frame_size * 144000) / (sample_rate << s->lsf); |
| 87 | frame_size += padding; |
| 88 | break; |
| 89 | } |
| 90 | s->frame_size = frame_size; |
| 91 | } else { |
| 92 | /* if no frame size computed, signal it */ |
| 93 | return 1; |
| 94 | } |
| 95 | |
| 96 | #if defined(DEBUG) |
| 97 | av_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ", |
| 98 | s->layer, s->sample_rate, s->bit_rate); |
| 99 | if (s->nb_channels == 2) { |
| 100 | if (s->layer == 3) { |
| 101 | if (s->mode_ext & MODE_EXT_MS_STEREO) |
| 102 | av_dlog(NULL, "ms-"); |
| 103 | if (s->mode_ext & MODE_EXT_I_STEREO) |
| 104 | av_dlog(NULL, "i-"); |
| 105 | } |
| 106 | av_dlog(NULL, "stereo"); |
| 107 | } else { |
| 108 | av_dlog(NULL, "mono"); |
| 109 | } |
| 110 | av_dlog(NULL, "\n"); |
| 111 | #endif |
| 112 | return 0; |
| 113 | } |
| 114 | |
| 115 | int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id) |
| 116 | { |
| 117 | MPADecodeHeader s1, *s = &s1; |
| 118 | |
| 119 | if (ff_mpa_check_header(head) != 0) |
| 120 | return -1; |
| 121 | |
| 122 | if (avpriv_mpegaudio_decode_header(s, head) != 0) { |
| 123 | return -1; |
| 124 | } |
| 125 | |
| 126 | switch(s->layer) { |
| 127 | case 1: |
| 128 | *codec_id = AV_CODEC_ID_MP1; |
| 129 | *frame_size = 384; |
| 130 | break; |
| 131 | case 2: |
| 132 | *codec_id = AV_CODEC_ID_MP2; |
| 133 | *frame_size = 1152; |
| 134 | break; |
| 135 | default: |
| 136 | case 3: |
| 137 | *codec_id = AV_CODEC_ID_MP3; |
| 138 | if (s->lsf) |
| 139 | *frame_size = 576; |
| 140 | else |
| 141 | *frame_size = 1152; |
| 142 | break; |
| 143 | } |
| 144 | |
| 145 | *sample_rate = s->sample_rate; |
| 146 | *channels = s->nb_channels; |
| 147 | *bit_rate = s->bit_rate; |
| 148 | return s->frame_size; |
| 149 | } |
| 150 | |
| 151 | int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate) |
| 152 | { |
| 153 | return avpriv_mpa_decode_header2(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id); |
| 154 | } |