So this is a “soft” sequential access limitation (we can tolerate some random writes to data as long as it is small enough and short enough). I wonder if there are formats that result in finished indexed multimedia file with “hard” sequential access, when nothing can be overwritten.
Digital video tape formats (e.g. DV, HDV) are an example. Other containers that operate in this mode are TS and Ogg (and optionally, MKV). Any sort of live streaming format generally is, too.
