Python library to split and join mp3 files

Question

There are a lot of libs to work with mp3 tags, but I need just 2 functions - split mp3 file in 2 parts and the second one to merge 5 mp3.

Can you suggest anything? Thanks!

Answer 1

Have a look at the MP3 file structure on Wikipedia. Use binary read mode in python to edit the MP3 file. s = open(file_name, 'rb').read() will put the whole file into a string object representing the raw bytes in your file (e.g. \xeb\xfe\x80). You can then search and edit the string, addressing the byte offsets with indices using brackets: s[n]. Finally, just do a binary write of the MP3 frames you want in your new file(s), appending the ID3 header to the set of frames that you want to make up each file.

Answer 2

I wrote a library (pydub) for pretty much this exact use case:

from pydub import AudioSegment

sound = AudioSegment.from_mp3("/path/to/file.mp3")

# len() and slicing are in milliseconds
halfway_point = len(sound) / 2
second_half = sound[halfway_point:]

# Concatenation is just adding
second_half_3_times = second_half + second_half + second_half

# writing mp3 files is a one liner
second_half_3_times.export("/path/to/new/file.mp3", format="mp3")

Adding a silent gap

If you'd like to add silence between parts of a sound:

two_sec_silence = AudioSegment.silent(duration=2000)
sound_with_gap = sound[:1000] + two_sec_silence + sound[1000:]

Answer 3

Here is my attempt at splitting an MP3 using python without re-encoding. Not all varieties of MP3 files are supported and I would gladly welcome suggestions or improvements. The script is hard coded to split at 55 seconds but the code demonstrates the general principles.

from __future__ import print_function
import struct
import sys

#MP3 frames are not independent because of the byte reservoir. This script does not account for
#that in determining where to do the split.

def SplitMp3(fi, splitSec, out):

    #Constants for MP3
    bitrates = {0x0: "free", 0x1: 32, 0x2: 40, 0x3: 48, 0x4: 56, 0x5: 64, 0x6: 80, 0x7: 96, 0x8: 112,
        0x9: 128, 0xa: 160, 0xb: 192, 0xc: 224, 0xd: 256, 0xe: 320, 0xf: "bad"}
    freqrates = {0x0: 44100, 0x1: 48000, 0x2: 32000, 0x3: "reserved"}
    countMpegFrames = 0
    frameDuration = 0.026
    unrecognizedBytes = 0
    splitFrame = int(round(splitSec / frameDuration))

    while True:

        startPos = fi.tell()

        #Check for 3 byte headers
        id3Start = fi.read(3)
        if len(id3Start) == 3:

            if id3Start == b'TAG':
                print ("Found ID3 v1/1.1 header")
                fi.seek(startPos + 256)
                continue

            if id3Start == b'ID3':
                #Possibly a ID3v2 header
                majorVer, minorVer, flags, encSize = struct.unpack(">BBBI", fi.read(7))
                if majorVer != 0xFF and minorVer != 0xFF:
                    encSize1 = (encSize & 0x7f000000) >> 24
                    encSize2 = (encSize & 0x7f0000) >> 16
                    encSize3 = (encSize & 0x7f00) >> 8
                    encSize4 = (encSize & 0x7f)
                    if encSize1 < 0x80 and encSize2 < 0x80 and encSize3 < 0x80 and encSize4 < 0x80:
                        size = ((encSize & 0x7f000000) >> 3) + ((encSize & 0x7f0000) >> 2) + ((encSize & 0x7f00) >> 1) + (encSize & 0x7f)
                        unsync = (flags >> 7) & 0x1
                        extendedHeader = (flags >> 6) & 0x1
                        experimental = (flags >> 5) & 0x1
                        print ("Found ID3v2 header")
                        print ("version", majorVer, minorVer, unsync, extendedHeader, experimental)
                        print ("size", size)
                        #TODO extendedHeader not supported yet

                        fi.seek(startPos + 10 + size)
                        continue

        #Check for 4 byte headers
        fi.seek(startPos)
        headerRaw = fi.read(4)
        if len(headerRaw) == 4:
            headerWord = struct.unpack(">I", headerRaw)[0]

            #Check for MPEG-1 audio frame
            if headerWord & 0xfff00000 == 0xfff00000:
                print ("Possible MPEG-1 audio header", hex(headerWord))
                countMpegFrames += 1
                ver = (headerWord & 0xf0000) >> 16
                bitrateEnc = (headerWord & 0xf000) >> 12
                freqEnc = (headerWord & 0xf00) >> 8
                mode = (headerWord & 0xf0) >> 4
                cpy = (headerWord & 0xf)
                if ver & 0xe == 0xa and freqEnc != 0xf:
                    print ("Probably an MP3 frame")
                    bitrate = bitrates[bitrateEnc]
                    freq = freqrates[freqEnc >> 2]
                    padding = ((freqEnc >> 1) & 0x1) == 1
                    print ("bitrate", bitrate, "kbps")
                    print ("freq", freq, "Hz")
                    print ("padding", padding)
                    frameLen = int((144 * bitrate * 1000 / freq ) + padding)

                    #Copy frame to output
                    fi.seek(startPos)
                    frameData = fi.read(frameLen)
                    if countMpegFrames >= splitFrame:
                        out.write(frameData)

                    fi.seek(startPos + frameLen)
                    continue
                else:
                    raise RuntimeError("Unsupported format:", hex(ver), "header:", hex(headerWord))

        #If no header can be detected, move on to the next byte
        fi.seek(startPos)
        nextByteRaw = fi.read(1)
        if len(nextByteRaw) == 0:
            break #End of file
        unrecognizedBytes += 1

    print ("unrecognizedBytes", unrecognizedBytes)
    print ("countMpegFrames", countMpegFrames)
    print ("duration", countMpegFrames * frameDuration, "sec")

if __name__=="__main__":
    fi = open(sys.argv[1], "rb")
    out = open("test.mp3", "wb")
    SplitMp3(fi, 55.0, out)
    out.close()

Merging would be a similar case of extracting and appending frames from two separate MP3 input files.

Answer 4

use the unix split command:

split -b 200k file.mp3 output_

this will output output_a, output_b, output_c, ..

you can then get mp3 files just by renaming

for file in ./output_*; do mv "$file" "$(basename $file).mp3"; done

this will output output_a.mp3, output_b.mp3, output_c.mp3 ... all of them (except the last one, may be) are 200kb in size, and the total size of the output_x is the same as file.mp3

you can use the du (disk usage) command to get the file's number of byte and then decide how many bytes to cut..

du -sh file.mp3

then to join use the cat command:

cat output_2.mp3 output_3.mp3 output_4.mp3 > output.mp3

of course you can put all this in a shell script and call it from python.

Answer 5

Check out GStreamer and its Python wrapper Gst-Python.