Codec for spotify offline files

[gijswijs]

I'm thinking about creating a codec for rockbox.
I have a premium Spotify account, so I can download spotify tracks to listen them offline.

This is what i think needs to be done:
- Reverse-engineer the system the normal Spotify client uses to store offline playlist and tracks. (I found out spotify stores it's cache per song in AppData\Local\Spotify\storage; If you want songs to be available offline spotify downloads the entire song as if it's cached entirely as far as I can see it. The files in storage have a gui as filename:
20123a445c4e6d86712ac9987e472e34817dadc6.file
- The files are stored encoded, but with the despotify library (http://despotify.se/) it should be possible to  decode the files to the native Spotify format which is Ogg
- Port the part of despotify that decodes the filestream as a audio codec in Rockbox
- be happy!

Before I embark on this (for me) far fetched journey into unknown technical territories I would really appreciate it if you guys could share some thoughts on the subject with me.

P.S. another possibility is to create a desktop program that encodes the spotify offline files to Ogg and than moving them to the player. That would make it unnecessary to create a codec. So that's plan B.

[saratoga]

We already support playing Ogg, but patches to do things like support DRM will not be accepted.

[dreamlayers]

See http://www.rockbox.org/wiki/NoDo for a short explanation on why DRM won't be supported.

Anyways, even if DRM was supported, I wouldn't recommend decoding DRM on a portable player.   DRM decoding is additional CPU activity which results in more power usage and shorter battery life.  This has been measured and documented on devices which are designed for DRM and using their original firmware.  So, just decode the DRM on your computer, if you can.