This is a reasonably simple tool for syncing a directory of music to some MTP device.
It tries to optimise bandwidth-wise by identifying sources using modification times and file sizes.

-m dir
  will sync dir onto the device; removing tracks from the device that aren't in the directory, and copying
  tracks onto the device which aren't there already - uniqueness is determined by equal modification times
  and file sizes.

-p dir
  will create a playlist on the device for each directory under dir. it'll also remove any playlists currently
  on the device. each playlist points at all files under the relevant directory - identified by modification
  time and file sizes.

The order of arguments is important - `hmtps -p foo -m bar` means to create the playlists before syncing the
music, which is usually useless (it won't point playlists to songs not on the device). `hmtps -m bar -m baz`
means to sync it twice - first with the bar directory, then baz (again useless, as it will just waste time
unless bar and baz are equivalent in the song set).

A useful setup might be to set up a few "profile" directories, each with symbolic links to perhaps some trees
in a global music directory, so that the set of songs on the device can easily be changed (./hmtps doesn't
care about filenames - only modification times and file sizes, so won't waste time deleting and reuploading
files already on there from the previous profile)

It might not be very useful if you often copy music off the device, as it stores all songs under one directory
with their names their modification times and sizes.

There's a chance that two different tracks might have the same file size and modification time .. `hmtps -m`
should warn if it finds these apparent duplicates - the modification time should be reset for both (but make
sure they still differ).