This is impossible.
MP3 audio is grouped into frames. Each frame contains 23 mSec of
audio data (and thus all MP3 files play at approximately 38 frames/
second).
If the MP3 is encoded at a high bit rate, each frame is large. If
it's encoded at a low bit rate, the frames are small. But they
always contain 23 mSec of audio.
Furthermore, the meaning of the data bytes in each frame depend on
the values in the frame header. If you change the header, the MP3
decoder won't have a clue how to decode the data in the frame. It
will fail miserably.
You can change values in the header, but that will just cause the MP3
decoder to fail. It won't change the fact that each frame contains
23 mSec of audio.
There are some techniques that will slow down audio to half or
quarter speed, but you have to do them downstream of the MP3
decoder. You can clock the audio driver at half or quarter speed, or
you can duplicate every sample of decoded audio by a factor of 2 or
4. But you can't do these things in Flash because you can't get your
hands on the decoded audio stream or the audio driver configuration.
-jeff stearns
On Jul 20, 2006, at 1:05 PM, Marc Hoffman wrote:
I've been using Flash to play back bird songs from amy website. By
generating some MP3's at half or quarter speed (with commensurate
drop in pitch) I can demonstrate some fascinating detail in bird
songs that's otherwise missed by the human ear.
Now if I could just modify the MP3 headers on-the-fly (with server
side file manipulation), I could let Flash slow down any MP3's
without having to generate and store separate versions of the sound
file on the server.
Anybody know of tools to modify MP3 header info on the fly? Sort of
like creating thumbnails of images using PHP?
Marc Hoffman
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