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libavformat/pcm.c

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00001 /*
00002  * PCM common functions
00003  * Copyright (c) 2003 Fabrice Bellard
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/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 }
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