GetChannel

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GetChannel(clip clip, int ch1 [, int ch2, ...] )
GetLeftChannel(clip clip)
GetRightChannel(clip clip)

  • GetChannel returns one or more channels of a multichannel signal.
  • GetLeftChannel returns the left and GetRightChannel the right channel from a stereo signal.
  • GetChannels is an alias to GetChannel and can be used interchangeably.


The ordering of the channels is determined by the ordering of the input file, because AviSynth doesn't assume any ordering (see Remarks).

In case of WAV files, the ordering should be as follows:

  WAV, 2 channels (stereo) 
1 left channel
2 right channel
  WAV, 5.1 channels 
2 front right channel
3 front center channel
4 LFE (Low Frequency Enhancement; Subwoofer)
5 rear left channel
6 rear right channel

Examples

  • Removes right channel information, and return as mono clip with only left channel:
video = AviSource("c:\filename.avi")
stereo = WavSource("c:\afx-ab3_t4.wav")
mono = GetLeftChannel(stereo)
return AudioDub(video, mono)
  • Do the same, alternate syntax:
video = AviSource("c:\filename.avi")
stereo = WavSource("c:\afx-ab3_t4.wav")
mono = GetChannel(stereo, 1)
return AudioDub(video, mono)
  • You could also obtain the channels from the AVI file itself:
video = AviSource("c:\filename.avi")
return GetChannel(video, 1)
  • Converts AVI with 5.1 audio to a stereo signal

(But see below for channel ordering, and here for more complex downmix functions.)

video = AviSource("c:\divx_51.avi")
stereo = GetChannel(video, 1, 2)
return AudioDub(video, stereo)
  • Converts AVI with "uncompressed 5.1 wav" audio to a stereo signal:
video = AviSource("c:\divx_wav.avi")
audio = WavSource("c:\divx_wav.avi")
stereo = GetChannel(audio, 1, 2)
return AudioDub(video, stereo)

Remarks

Every file format has a different internal channel ordering. The following table gives this internal ordering for some formats (useful for plugin writers), but it is the decoder's task to return the expected (WAV) channel order. If you use decoders like NicAudio/BassAudio or ffdshow/AC3_filter you don't need to worry about this.

Format Channel 1 Channel 2 Channel 3 Channel 4 Channel 5 Channel 6
5.1 WAV front left channel front right channel front center channel  LFE rear left channel rear right channel
5.1 AC3 front left channel front center channel  front right channel rear left channel rear right channel  LFE
5.1 DTS front center channel  front left channel front right channel rear left channel rear right channel LFE
5.1 AAC front center channel  front left channel front right channel rear left channel rear right channel LFE
5.1 AIFF front left channel rear left channel front center channel  front right channel  rear right channel LFE
5.1 FLAC front left channel front right channel front center channel  LFE rear left channel rear right channel 
5.1 WMA   front left channel front right channel front center channel  LFE rear left channel rear right channel 
  • 5.1 DTS: the LFE is on a separate stream (much like on multichannel MPEG2).
  • A free version of the AAC specifications are unavailable online.
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