CODEWITHSUNDEEP
pythonmp3binaryfileslame
fexplorer
fexplorer

Reputation: 43

How to read specific bytes from a binary MP3 file in Python?

I would learn to handle read and write binary data. I know that I can open a binary file with

f = open(myfile, mode='rb')
fb = f.read()
f.close()
return fb

How can I access and read the range $A7-$AC in a mp3 file with this structure: Lame mp3 Tags

Upvotes: 1

Views: 3040

Answers (1)

Martin Evans
Martin Evans

Reputation: 46759

You should take a look at Python's struct library for help with extracting binary data.

import struct

mp3_filename = r"my_mp3_file.mp3"

with open(mp3_filename, 'rb') as f_mp3:
    mp3 = f_mp3.read()
    entry = mp3[0xA7:0xAC+1]
    print struct.unpack("{}b".format(len(entry)), entry)

This would give you a list of integers such as:

(49, 0, 57, 0, 57, 0)

You pass a format string to tell Python how to intepret each of the bytes. In this example, they are all simply converted from bytes into integers. Each format specifier can have a repeat count, so for your example, the format string would be "6b". If you wanted to decode this as words, you would simply change the format specifier, there is a full table of options to help you: Struct format characters

To convert these to zeros, you would need to close the file and reopen it for writing. Build a new output as follows:

import struct

mp3_filename = r"my_mp3_file.mp3"
zeros = "\0\0\0\0\0\0"

with open(mp3_filename, 'rb') as f_mp3:
    mp3 = f_mp3.read()
    entry = mp3[0xA7:0xAC+1]
    print struct.unpack("{}B".format(len(entry)), entry)

    if entry != zeros:
        print "non zero"

with open(mp3_filename, 'wb') as f_mp3:
    f_mp3.write(mp3[:0xA7] + zeros + mp3[0xAD:])

FYI: There are ready made Python libraries that are able to extract tag information from MP3 files. Take a look at something like the id3reader package.

Upvotes: 1

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