thoughton:digitallife PCM to MPEG1 to AIFF to AC3

PCM to MPEG1 to AIFF to AC3

I recently encountered an unusual AVI video file, containing MSMPEG4 video and PCM audio. My favorite DVD (ffmpeg) preset in ffmpegX refused to process the file. I knew from previous experience that the DVD (ffmpeg) preset could handle MSMPEG4 video, so I surmised it was the PCM audio that was fouling things up.

Slower workaround
I worked around the problem by using the DVD (mpeg2enc) preset with 'Decode with mplayer' selected. After a slow encode (probably twice as long as ffmpeg) I ended up with an .mpv video file and another file. This second file had a truncated name, according to the settings it should have been some sort of AC3, but the mpeg2enc engine had produced a file without a suffix.

Not actually an AC3 at all
The first thing I did was drop the mystery file onto ffmpegX for identification but, unusually for ffmpegX, nothing was revealed. I then tried adding an .ac3 suffix only to have A.Pack reject the file. Soldiering on, I changed it to .mp2 and tried to open it in QuickTime Player. Still no go :mad: . Finally I tried an .mpa suffix. Bingo! Hitting command-J showed that QuickTime identified the file as an MPEG1 audio file. Unfortunately my good mood was short-lived. I was unable to export it from QuickTime - the only options were movie formats.

MPEG1?
After resorting to Google I was reminded that iTunes can play MPEG1 audio files. The first thing I did was change the iTunes import preferences to 'AIFF encoder'. However iTunes then refused to let me drag my .mpa file into the music library unless I changed the suffix to .mp2. Once I had done that I used iTunes to convert the audio file to AIFF (by option-clicking the Advanced menu and choosing 'convert to AIFF').

The Finish Line
Once I had my AIFF, I was able to drop it into A.Pack, select my two channels, and convert it into a two channel AC3 file. From there it was just a matter of using the .mpv video file and .ac3 audio file in Sizzle to author a DVD, and using Toast to burn it.

Conclusions
The Mac used to boast a system where, no matter what you changed the name of a file to, double clicking it would always open the correct application. We used to brag about this to PC users. Why am I now, fifteen years later, messing around changing file extensions?

Posted on 22 January 2005, to How To... | Mac Audio | Mac Video