OK, perhaps, the thread has wandered slightly off course, but this is my take - and it's hypothetical only.

To evaluate, I created a 32 bar song, 3 repeats, using RealTracks (_JazFred.sty).
Saved, but Not generated. File size: 3292 bytes
Generate song and save. File size: 3292 bytes
Freeze tracks and Save, File size: 114656 bytes

The frozen song size of 114656 bytes cannot realistically contain much audio data in such a small file.

So, back to my theory:

RealTracks are made up of multiple sound 'phrases' played by musicians. Each phrase may be multiple bars in length.

When you generate, BiaB uses an algorithm to decide which phrases to 'glue together' to make up the entire song. It doesn't need to remember which phrases it used, because next time you generate, it (usually) produces a different set of phrases.

However, if you freeze the tracks, BiaB needs to store exactly which phrases had been used in the previous generation, so it can glue them together in the correct sequence and therefore repeat the performance, note-for-note.

The extra data in the file is a template of exactly which phrases were used to make up the now frozen song.

So there is still a requirement to select all of the required audio phrases and 'glue them back together', and that takes time.

So playing a song that has been frozen does not guarantee instant playback. Of course, the regeneration is handled in a separate thread, so playback can start once the software has decided that it has enough headway to complete the background generation before running out of buffers, and that's why on slower machines there is an option to turn off "Speed up generation of RealTracks" (incidentally, is this option available on a Mac?)

So I think that the song actually gets 'generated' every time, meaning that the audio phrases still need to be extracted and glued together. Maybe Mac's do this without the separate generate thread?

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