Decoders
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Decoders are configured elements in Libav which allow the decoding of multimedia streams.

When you configure your Libav build, all the supported native decoders are enabled by default. Decoders requiring an external library must be enabled manually via the corresponding --enable-lib option. You can list all available decoders using the configure option --list-decoders.

You can disable all the decoders with the configure option --disable-decoders and selectively enable / disable single decoders with the options --enable-decoder=DECODER / --disable-decoder=DECODER.

The option -decoders of the av* tools will display the list of enabled decoders.

Audio Decoders
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A description of some of the currently available audio decoders follows.

ac3
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AC-3 audio decoder.

This decoder implements part of ATSC A/52:2010 and ETSI TS 102 366, as well as the undocumented RealAudio 3 (a.k.a. dnet).

AC-3 Decoder Options
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-drc_scale VALUE
     Dynamic Range Scale Factor. The factor to apply to dynamic range values from the AC-3 stream. This factor is applied exponentially. There are 3 notable scale factor ranges:

     drc_scale == 0
          DRC disabled. Produces full range audio.

     0 < drc_scale <= 1
          DRC enabled.  Applies a fraction of the stream DRC value. Audio reproduction is between full range and full compression.

     drc_scale > 1
          DRC enabled. Applies drc_scale asymmetrically. Loud sounds are fully compressed.  Soft sounds are enhanced.