CODEWITHSUNDEEP
pythonmp3
user1167192
user1167192

Reputation: 55

Python split mp3 channel

I'd like to seperate the channels of a mp3 file in Python and save it in two other files. Does anybody know a library for this. Thanks in advance.

Upvotes: 3

Views: 1981

Answers (2)

Anna Andreeva Rogotulka
Anna Andreeva Rogotulka

Reputation: 1624

The left and right channels are separated from the loaded audio array with librosa, the separated channels are saved as new audio files using soundfile

import librosa
import soundfile as sf

input_file_path = "your_input_file.mp3"
output_left_path = "output_left.wav"
output_right_path = "output_right.wav"

audio, sr = librosa.load(input_file_path, sr=None, mono=False)

# separate channels
left_channel = audio[0, :]
right_channel = audio[1, :]

# save
sf.write(output_file_left, left_channel, sr)
sf.write(output_file_right, right_channel, sr)

Upvotes: 1

Tankman六四
Tankman六四

Reputation: 1778

I assume you want to split the channels losslessly, without decoding MP3 and re-encoding it - otherwise you would not have mentioned MP3 at all and would have easily found many tools like Audacity to do that.

There are 4 channel modes of MP3 frames - this means 4 types of MP3 files: simple stereo, joint-stereo, dual-channel, mono. joint-stereo files can't be split without loss. mono files doesn't need splitting. The rest: stereo and dual-channel, consists of less than 0.1% of all MP3 files, technically can be split into 2 files, each for a channel, without loss. However there is not any tool on the Internet to do that - not any command line tool nor any GUI tool, because few need the function.

There are not any python library for you neither. Most libraries abstracted MP3 files into a common audio which you can manipulate, after decoding. pymad is the only one specific to MP3 file, and it can tell if a file is using any of the 4 channel modes, but does not offer to extract a channel without decoding it. If you write a new tool, you will have to work on raw MP3 files or produce a library for it.

And it is not easy to write a tool or library for it. It's one stream with 2 channels and not two streams interleaved on a frame level. You cannot simply work on MP3 frames, drop some frames, keep others, and manage to extract a channel out that way. It's a task for a professional, and perhaps best happen in a decoder project (like lame or libmad) and not in a file manipulation project (like mp3info or the python eyeD3). In other words, this feature is likely written in C, not python.

Implementaiton Note:

The task to build such a tool thus suits well for a computer science C-programming language course project: 1. it takes a lot of time to do; 2. it requires every skill learned from C programming course; 3. it can get wrong easily; 4. it is likely built on the work of other projects, a lesson of adaptating existing work; 5. is a damn-hard endeavor that no-one did before and thus very rewarding 6. perhaps can be done in 300 difficult lines of code instead of bloated simple Visual Basic code, thus is a good lession of modesty and quality; 7. and finally: nobody is waiting in an hurry for a working implementation.

All condition fits perfectly for a C-programming course project.

Implementation Note 2:

some bit-rates are only possible in mono mode (80kbps), and some bit-rates are only possible in stereo mode (e.g. 320kpbs). Luckily this does not present a problem in this task, because all dual-mp3 bit-rate can be mapped into a fitting mono-mp3 bit-rate -- but not vice versa!

Upvotes: 3

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