why do people convert a ac3 to mp3

[gavogavo]

Why not just convert it to ac3 192kb at 2 channels wont it sound better cause your not going from lossy codec to another? Or is ac3 just bad at low bitrates even at 128?

[Inspector.Gadget]

Transcoding lossy to lossy is always going to result in quality loss. AFAIK MP3 is more efficient per bit for stereo sources than AC3, thus AC3 to MP3 is probably better than AC3 to AC3 where there's more than a minimal amount of audio data to be encoded.

[Ghitulescu]

Because they want space and don't care about the quality (they do not sense any notable difference). Also most players can easily MP2/3 but not all of then can do AC-3.

[Blue_MiSfit]

AC3 retains full frequency response for 2ch content at 192kbps. Below this, it begins to lowpass (cut high frequencies). As we all know, 128kbps MP3 can sound reasonably good for 2ch content, but AC3 would sound quite bad. DD+/EC3 is another story...

The same holds true for 5.1ch content at 448kbps IIRC. 384 is commonly used because it doesn't pull too much off the high end.

That being said, the only reason to transcode AC3 to 2ch MP3 for a DVD backup are:

A) You are really desperate for space
AND
B) You can't use something nicer (like AAC), either due to hardware restrictions, or "scene" rules, in which case you shouldn't be posting on doom9 ;)

Also, transcoding is still transcoding. AC3 -> AC3 is not really inherently better than AC3 -> MP3.

If you're going to transcode it, you should at least use something more efficient than AC3.

~MiSfit