Tag Archives: audio

Adding AC3 Dolby Digital 5.1 multichannel audio to an MP4 without re-encoding

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I recently “obtained” some video files which had 5.1 surround sound encoded as AAC, but AppleTV does not play multichannel audio in AAC format.

While AppleTV can play back stereo or Dolby Pro Logic II in AAC format, it requires multichannel audio be encoded as AC3. None of these “acquired” MP4s have AC3 5.1 6-channel audio!

I could encode the file again, but that takes to much time. Is there a way I can just add or import AC3 multichannel audio to my existing video files?

The short answer is yes.

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Mute system audio when increasing/decreasing volume

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Here’s a cool tip from The Distant Librarian on how to silence the audio feedback you get when using the keyboard to increase or decrease the volume in Mac OS X.

Hold down the shift key while depressing the volume keys will silence the auditory feedback while raising and lowering the volume, but still show the visual cue.

Other cool tricks:

Hold down option while clicking one of the sound keys to access the Sound system preferences.

Get more granular volume control by holding down shift-option while clicking one of the sound keys to increase/decrease volume in 1/4 the normal increments. Normal, the Mac provides 16 volume levels. Holding down shift-option gives you 64 increments.