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Goal: automatically adjusting speed (bpm) of a given set of MP3 files in order to have a collection of music optimized to be heard when I am running. (I realized that I prefer to run with about 168 bpm in my ears).

Of course, I could have some software to detect BPM and then calculate and stretch/squeeze each song using Audacity or a similar tool, however, I'd prefer a solution which requires less manual operation.

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First, find software to detect the BPM. Then, sox. – Ignacio Vazquez-Abrams Dec 11 '10 at 12:56
Hey, sox is a cool tool - thanks :) Still, it would be quite time consuming this way, I hoped for a solution which is as automated as possible. I think I'll have some more research, maybe I find a BPM detector with command line interface, so I could write a script to glue them together :) Thanks a lot – Peter P Dec 12 '10 at 19:47

I think soundstretch has the requirements. Command line based, it adjustes the song to the desired BPM. Try it because sometimes it estimates the wrong number of beats (rarely, it seems)

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Further, use ffmpeg or similar to convert between WAV and MP3. – Mechanical snail Jul 6 '12 at 21:18

Try Mixxx.

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Thanks for pointing out this cool piece of software. Unfortunately, it cannot help in achieving my goal, but interesting program nevertheless :) – Peter P Dec 12 '10 at 19:44

I use Audacity. It's free, open-source, and can load and save mp3 or almost anything directly. Use the Change Tempo effect.

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