The fastest checksum algorithm I can seem to find is Adler32 (defined within RFC1950), which is far from cryptographically secure, but should suffice for this task, if you were to decide to implement it.

I must add that it might be a good idea to only hash/checksum the MP3 portion of the file, as changes in ID3 tags might not necessitate reuploading the whole file. Maybe have a toggle or ask or have a way to just update the tags. Whatever.