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libavcodec/flac.c

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00001 /*
00002  * FLAC common code
00003  * Copyright (c) 2009 Justin Ruggles
00004  *
00005  * This file is part of Libav.
00006  *
00007  * Libav is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * Libav is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with Libav; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00022 #include "libavutil/crc.h"
00023 #include "flac.h"
00024 #include "flacdata.h"
00025 
00026 static const int8_t sample_size_table[] = { 0, 8, 12, 0, 16, 20, 24, 0 };
00027 
00028 static int64_t get_utf8(GetBitContext *gb)
00029 {
00030     int64_t val;
00031     GET_UTF8(val, get_bits(gb, 8), return -1;)
00032     return val;
00033 }
00034 
00035 int ff_flac_decode_frame_header(AVCodecContext *avctx, GetBitContext *gb,
00036                                 FLACFrameInfo *fi, int log_level_offset)
00037 {
00038     int bs_code, sr_code, bps_code;
00039 
00040     /* frame sync code */
00041     if ((get_bits(gb, 15) & 0x7FFF) != 0x7FFC) {
00042         av_log(avctx, AV_LOG_ERROR + log_level_offset, "invalid sync code\n");
00043         return -1;
00044     }
00045 
00046     /* variable block size stream code */
00047     fi->is_var_size = get_bits1(gb);
00048 
00049     /* block size and sample rate codes */
00050     bs_code = get_bits(gb, 4);
00051     sr_code = get_bits(gb, 4);
00052 
00053     /* channels and decorrelation */
00054     fi->ch_mode = get_bits(gb, 4);
00055     if (fi->ch_mode < FLAC_MAX_CHANNELS) {
00056         fi->channels = fi->ch_mode + 1;
00057         fi->ch_mode = FLAC_CHMODE_INDEPENDENT;
00058     } else if (fi->ch_mode <= FLAC_CHMODE_MID_SIDE) {
00059         fi->channels = 2;
00060     } else {
00061         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00062                "invalid channel mode: %d\n", fi->ch_mode);
00063         return -1;
00064     }
00065 
00066     /* bits per sample */
00067     bps_code = get_bits(gb, 3);
00068     if (bps_code == 3 || bps_code == 7) {
00069         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00070                "invalid sample size code (%d)\n",
00071                bps_code);
00072         return -1;
00073     }
00074     fi->bps = sample_size_table[bps_code];
00075 
00076     /* reserved bit */
00077     if (get_bits1(gb)) {
00078         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00079                "broken stream, invalid padding\n");
00080         return -1;
00081     }
00082 
00083     /* sample or frame count */
00084     fi->frame_or_sample_num = get_utf8(gb);
00085     if (fi->frame_or_sample_num < 0) {
00086         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00087                "sample/frame number invalid; utf8 fscked\n");
00088         return -1;
00089     }
00090 
00091     /* blocksize */
00092     if (bs_code == 0) {
00093         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00094                "reserved blocksize code: 0\n");
00095         return -1;
00096     } else if (bs_code == 6) {
00097         fi->blocksize = get_bits(gb, 8) + 1;
00098     } else if (bs_code == 7) {
00099         fi->blocksize = get_bits(gb, 16) + 1;
00100     } else {
00101         fi->blocksize = ff_flac_blocksize_table[bs_code];
00102     }
00103 
00104     /* sample rate */
00105     if (sr_code < 12) {
00106         fi->samplerate = ff_flac_sample_rate_table[sr_code];
00107     } else if (sr_code == 12) {
00108         fi->samplerate = get_bits(gb, 8) * 1000;
00109     } else if (sr_code == 13) {
00110         fi->samplerate = get_bits(gb, 16);
00111     } else if (sr_code == 14) {
00112         fi->samplerate = get_bits(gb, 16) * 10;
00113     } else {
00114         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00115                "illegal sample rate code %d\n",
00116                sr_code);
00117         return -1;
00118     }
00119 
00120     /* header CRC-8 check */
00121     skip_bits(gb, 8);
00122     if (av_crc(av_crc_get_table(AV_CRC_8_ATM), 0, gb->buffer,
00123                get_bits_count(gb)/8)) {
00124         av_log(avctx, AV_LOG_ERROR + log_level_offset,
00125                "header crc mismatch\n");
00126         return -1;
00127     }
00128 
00129     return 0;
00130 }
00131 
00132 int ff_flac_get_max_frame_size(int blocksize, int ch, int bps)
00133 {
00134     /* Technically, there is no limit to FLAC frame size, but an encoder
00135        should not write a frame that is larger than if verbatim encoding mode
00136        were to be used. */
00137 
00138     int count;
00139 
00140     count = 16;                  /* frame header */
00141     count += ch * ((7+bps+7)/8); /* subframe headers */
00142     if (ch == 2) {
00143         /* for stereo, need to account for using decorrelation */
00144         count += (( 2*bps+1) * blocksize + 7) / 8;
00145     } else {
00146         count += ( ch*bps    * blocksize + 7) / 8;
00147     }
00148     count += 2; /* frame footer */
00149 
00150     return count;
00151 }
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