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  1. @chapter Decoders
  2. @c man begin DECODERS
  3. Decoders are configured elements in Libav which allow the decoding of
  4. multimedia streams.
  5. When you configure your Libav build, all the supported native decoders
  6. are enabled by default. Decoders requiring an external library must be enabled
  7. manually via the corresponding @code{--enable-lib} option. You can list all
  8. available decoders using the configure option @code{--list-decoders}.
  9. You can disable all the decoders with the configure option
  10. @code{--disable-decoders} and selectively enable / disable single decoders
  11. with the options @code{--enable-decoder=@var{DECODER}} /
  12. @code{--disable-decoder=@var{DECODER}}.
  13. The option @code{-decoders} of the av* tools will display the list of
  14. enabled decoders.
  15. @c man end DECODERS
  16. @chapter Audio Decoders
  17. @c man begin AUDIO DECODERS
  18. A description of some of the currently available audio decoders
  19. follows.
  20. @section ac3
  21. AC-3 audio decoder.
  22. This decoder implements part of ATSC A/52:2010 and ETSI TS 102 366, as well as
  23. the undocumented RealAudio 3 (a.k.a. dnet).
  24. @subsection AC-3 Decoder Options
  25. @table @option
  26. @item -drc_scale @var{value}
  27. Dynamic Range Scale Factor. The factor to apply to dynamic range values
  28. from the AC-3 stream. This factor is applied exponentially.
  29. There are 3 notable scale factor ranges:
  30. @table @option
  31. @item drc_scale == 0
  32. DRC disabled. Produces full range audio.
  33. @item 0 < drc_scale <= 1
  34. DRC enabled. Applies a fraction of the stream DRC value.
  35. Audio reproduction is between full range and full compression.
  36. @item drc_scale > 1
  37. DRC enabled. Applies drc_scale asymmetrically.
  38. Loud sounds are fully compressed. Soft sounds are enhanced.
  39. @end table
  40. @end table
  41. @c man end AUDIO DECODERS