pcm.c 2.0 KB

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  1. /*
  2. * PCM common functions
  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/mathematics.h"
  22. #include "avformat.h"
  23. #include "pcm.h"
  24. int pcm_read_seek(AVFormatContext *s,
  25. int stream_index, int64_t timestamp, int flags)
  26. {
  27. AVStream *st;
  28. int block_align, byte_rate;
  29. int64_t pos, ret;
  30. st = s->streams[0];
  31. block_align = st->codec->block_align ? st->codec->block_align :
  32. (av_get_bits_per_sample(st->codec->codec_id) * st->codec->channels) >> 3;
  33. byte_rate = st->codec->bit_rate ? st->codec->bit_rate >> 3 :
  34. block_align * st->codec->sample_rate;
  35. if (block_align <= 0 || byte_rate <= 0)
  36. return -1;
  37. if (timestamp < 0) timestamp = 0;
  38. /* compute the position by aligning it to block_align */
  39. pos = av_rescale_rnd(timestamp * byte_rate,
  40. st->time_base.num,
  41. st->time_base.den * (int64_t)block_align,
  42. (flags & AVSEEK_FLAG_BACKWARD) ? AV_ROUND_DOWN : AV_ROUND_UP);
  43. pos *= block_align;
  44. /* recompute exact position */
  45. st->cur_dts = av_rescale(pos, st->time_base.den, byte_rate * (int64_t)st->time_base.num);
  46. if ((ret = avio_seek(s->pb, pos + s->data_offset, SEEK_SET)) < 0)
  47. return ret;
  48. return 0;
  49. }