00001 /* 00002 * PCM common functions 00003 * Copyright (c) 2003 Fabrice Bellard 00004 * 00005 * This file is part of FFmpeg. 00006 * 00007 * FFmpeg 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 * FFmpeg 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 FFmpeg; 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/mathematics.h" 00023 #include "avformat.h" 00024 #include "pcm.h" 00025 00026 int pcm_read_seek(AVFormatContext *s, 00027 int stream_index, int64_t timestamp, int flags) 00028 { 00029 AVStream *st; 00030 int block_align, byte_rate; 00031 int64_t pos, ret; 00032 00033 st = s->streams[0]; 00034 00035 block_align = st->codec->block_align ? st->codec->block_align : 00036 (av_get_bits_per_sample(st->codec->codec_id) * st->codec->channels) >> 3; 00037 byte_rate = st->codec->bit_rate ? st->codec->bit_rate >> 3 : 00038 block_align * st->codec->sample_rate; 00039 00040 if (block_align <= 0 || byte_rate <= 0) 00041 return -1; 00042 if (timestamp < 0) timestamp = 0; 00043 00044 /* compute the position by aligning it to block_align */ 00045 pos = av_rescale_rnd(timestamp * byte_rate, 00046 st->time_base.num, 00047 st->time_base.den * (int64_t)block_align, 00048 (flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP); 00049 pos *= block_align; 00050 00051 /* recompute exact position */ 00052 st->cur_dts = av_rescale(pos, st->time_base.den, byte_rate * (int64_t)st->time_base.num); 00053 if ((ret = avio_seek(s->pb, pos + s->data_offset, SEEK_SET)) < 0) 00054 return ret; 00055 return 0; 00056 }