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So I found an mp3 player the other day and I thought it'd be fun to try and reverse engineer the files I found on it (and maybe even try to modify it). When I plugged it in to my pc I was surprised to see more than just folders with mp3 files, I could see a few .LIB files named "AUDIBLE.LIB", "EBOOK.LIB", "M3U.LIB", "MUSIC.LIB", "MUSIC2.LIB", "PICTURE.LIB", "VIDEO.LIB". I wanted to see what they looked like so I tried to find out how to read .LIB files using google, however I did not succeed. I tried dumpbin, hxd and ida, but none of them worked (dumpbin said it was an invalid file format, hxd didn't help with finding a magic number and ida couldn't open it). Each file starts with the name of the file (eg: "PICTURE"), followed by some 00 bytes, the 8th byte is 01 and then come another 5 00 bytes followed by "ALLFILE". I'm new to reverse engineering so I'm sorry if this question is stupid, but how would I go about reverse engineering this?

File example (only the first few lines of bytes):

45 42 4F 4F 4B 00 00 00 01 00 01 00 00 00 00 00
41 4C 4C 46 49 4C 45 00 00 00 00 00 00 00 00 00
00 00 00 00 02 00 03 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

In case it matters, the mp3 player is a Xemio-240.

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  • I have a set of Bluetooth ear buds (Axloie S7) that have a GB of storage built in and also function as an mp3 player. There is a file that stays exactly 1,500KB no matter what I put on the drive titled “MUSIC.LIB” in the root of the drive. I will try to describe how it. Here is the first little chunk, minus the asterisks *MUSIC ALLSONG ALBUM ARTIST GENRE * Then a bunch of zeros Then metadata for each song with zeros in between Then a bunch of random characters that look like code or encrypted data Then *UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUULAME3.89 (beta)UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU
    – MaxUgly
    Mar 24, 2022 at 13:50

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I guess the files you found are index files. They contain the list of all pictures, ebooks, playlists (m3u) and so on, so the player doesn't have to open each individual file when you search for a specific song or video. This means these files are most like a custom database format. The first header line might be something like the "database name", and the second header line, always "ALLFILES" might be a "table name".

I don't recognize this file as the storage format of a well-known open-source database engine, but that would be the area where I suggest you to start researching. It might be a completely custom format, though.

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