To quote the site www.fileinfo.com, “AC-3 files, or Dolby Digital audio file format; may contain up to 6 channels of audio, including a subwoofer output (a.k.a. 5.1 surround sound)”

These have been referred to as  ”Audio Codec 3″ or “Advanced Codec 3″ or “Acoustic Codec 3.”

Regardless, this is the file format that was adapted for the audio portion of DVDs and Blu-ray discs.  Just like the mpeg2 files that make up the video portion of a  DVD or Blu-ray discs, the AC-3 files cannot be edited.  That was instituted on purpose of course, as an anti-piracy measure.

(As a side note, remember, in addition to not being able to edit mpeg2 or AC-3 files, you cannot drag those files as accessible elements from a DVD or Blu-ray video disc either: http://tinyurl.com/yj8wy3c)

The AC-3 format has the capacity to record audio with fidelity up to 48k, which is audio CD quality.

The AC-3 codec is also an efficient codec in that a number of audio channels (up to 6) can be included in just one AC-3 file.

The AC-3 files are actually located within the VIDEO_TS folders on the DVD or Blu-ray [see below].  (the BUP folders are backup folders, for use if the main TS folders cannot be accessed for some reason — like due to a minor scratch on the disc).

While you can get to the level of the DVD or Blu-ray architecture that is depicted above, by right clicking on the DVD icon in My Computer and choosing either Open or Explore, you won’t get any further down into the structure without some sort of “ripping” software.

When burning or authoring an edited video from a non-linear editing system on to DVD, the video of the final sequence needs to be converted to mpeg2 and the audio to AC-3.

In Final Cut Pro, that means exporting the edited sequence, which is usually in some form of .mov file, through the Apple Compressor software.  The resulting files can then be loaded into an authoring program, like DVD Studio Pro, Adobe Encore or Sonic Scenarist.

Some folks are not always pleased with the resulting files from Compressor, so they opt for outputting the edited sequence to a dital Betacam tape and then encode the videotape into a hardware encorder which also makes mpeg2 files and AC-3 files that can be loaded into an authoring system.

Again, remember, the mpeg2 and AC-3 files are not editable.

I welcome your feedback. Either write a comment below, or write me at dryan@videolabs.net

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