Python library to modify MP3 audio without transcoding

Question

I am looking for some general advice about the mp3 format before I start a small project to make sure I am not on a wild-goose chase.

My understanding of the internals o

Answer 1

I got three quality answers, and I thank you all (and upvoted you all) for them. I haven't chosen any as the accepted answer, because each addressed one aspect, so I wanted to write a summary.

Do you need to work in MP3?

• Transcoding to PCM and back to MP3 is unlikely to result in a drop in quality.

• Don't optimise audio-quality prematurely; test it with a simple prototype and listen to it.

Working in MP3

• Wikipedia has a summary of the MP3 File Format.

• MP3 frames are short (1152 samples, or just a few milliseconds) allowing for moderate precision at that level.

• However, Wikipedia warns that "Frames are not independent items ("byte reservoir") and therefore cannot be extracted on arbitrary frame boundaries."

• Existing libraries are unlikely to be of assistance, if I really want to avoid decoding.

Working in PCM

There are several libraries at this level:

• LAME (latest release: October 2017)
• PyMedia (latest release: February 2006)
• PyMad (Linux only? Decoder only? Latest release: January 2007)

Working at a higher level

• Echo Nest Remix API (Mac or Linux only, at the moment) is an API to a web-service that supports quite sophisticated operations (e.g. finding the locations of music beats and tempo, etc.)

• mp3DirectCut (Windows only) is a GUI that apparently performs the operations I want, but as an app. It is not open-source. (I tried to run it, got an Access Denied installer error, and didn't follow up. A GUI isn't suitably for me, as I want to repeatedly run these operations on a changing library of files.)

My plan is now to start out in PyMedia, using PCM. Thank you all for your assistance.