Sunday, January 20, 2008

FLASH: Mp3 player swf plays chipmunk sounds

Most mp3s are encoded at 128 and 192 kbps, but I was working on a project that used speech recordings, and speech is usually encoded at a lower bitrate than 128. I found every time I played the recording in a flash based mp3 player it played it too fast, making it sound like alvin and the chipmunks.

I went through and made a whole bunch of mp3s at different bitrates using the lame 3.96 encoder to see which were supported and which bitrates were not.
fixed bitrates:
:( 16 kbps
:( 24 kbps
:( 32 kbps
:( 40 kbps
:) 48 kbps
:( 56 kbps
:( 64 kbps
:( 80 kbps
:) 96 kbps
:) 112 kbps
:) 128 kbps
:) 160 kbps
:) 192 kbps
:) 224 kbps
:) 320 kbps

variable bitrates (with lame; 0 is high quality, 9 is low):
:) V0-6
:( V7-9


So the basic synopsis is mp3s encoded as 48kbps work and anything greater or equal to 96kbps also works. Everything else is not supported (is support, but sounds like chipmunks).
[EDITED]
see
http://www.summitsolutions.co.uk/blog/how-to-correct-the-chipmunk-effect-in-the-podpress-flash-player
for another possible explanation of the chipmunk sounds.

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