Think we're at cross purposes here.
I'm talking solely about downloading un-transcoded recordings which are generated only from SD channels and then those channels being immediately playable locally on a PC or other device without any fresh transcoding being needed. It may be that that same file can be transcoded without much (or any) noticeable loss into H264, and thus reduce file size significantly but I'm not interested in that.
Given the encrypted nature of HD broadcasts I never had any expectation that those recordings could be lifted off the box in their original format, and therefore transcoding on the box would always need doing.
I'll confirm the stream formats in a while when I've got some time to ftp across SD channel recordings and then identify the codecs via VLC or similar.