From other threads I've discovered that the generation of songs with RealTracks has two phases, one where a choice of what is to be played is made, and the other where the chosen elements are assembled into audio form before they're played.

What is stored when you "freeze" a track is the outcome of the first phase, and the second phase has to be performed each time the frozen song is opened afresh (as Noel96 says, the file is too small to hold the audio data).

I would expect such a frozen file to hold all the information that is needed for BIAB to reproduce the track whether on the computer it was created on, or on another computer which has the same set of RealTracks etc.

What I've found is that frozen files prepared on another computer don't behave in the same way on my computer as files I've prepared myself, in that the "Play" button causes BIAB to generate the RealDrums part, but not the RealTracks parts, so what is played back is the drums along with any MIDI parts that might have been left (we've been trying to replace all MIDI parts with RealTracks). I have to use Play=>Generate (even if tracks are frozen) to get these "foreign" files to work.

Obviously, we could decide to render our whole repertoire to WAV form, but we would lose the flexibility we have when running directly from BIAB.