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Available MP3 frequency rates and obtaining the Professional codec

Another common question I get is why VirtualDub can't encode MP3 above 56Kbps. Remember, VirtualDub has no audio encoding support of its own -- it relies solely on codec installed in the Windows Audio Compression Manager (ACM) to compress audio, and that usually means the Fraunhofer-IIS MP3 codec. (You may also have the Lame ACM and/or Creative MP3 codecs, but these are known to trigger hangs and crashes on some systems.) There are at least five major versions of the MP3 codec in existence:

All versions will decode any format, but because they all register under the entry "msacm.l3acm" only one can be installed at a time. What often happens is that some application will install and overwrite the entry with the Advanced codec, thus dropping your encoding capability to 56Kbps. This will break any older application that might have installed and relied on the Professional codec. Changing the l3acm entry back to l3codecp.acm under Drivers32 in system.ini (95/98/ME) or the Registry (NT/2000/XP) will restore the higher bandwidth modes.

The good news is that for those of you who have lost the Professional version, there is a safe and easy way to obtain it again: install Windows Media Player 10. This installs the recent revision of the Professional version that encodes up to 320Kbps.


This blog was originally open for comments when this entry was first posted, but was later closed and then removed due to spam and after a migration away from the original blog software. Unfortunately, it would have been a lot of work to reformat the comments to republish them. The author thanks everyone who posted comments and added to the discussion.