For example, you have a media file of size 20M and you wish to break it up to 10M chunk, just use the split command that comes with Linux
split -b 10M test-split.wmvConsequently, the command will break the test-split.wmv into 2 chunk xaa and xab. "xaa" and "xab" are generated by the split command. If you split into more chunk, it will follow the alphabetical order xac, xad etc
To join back the 2 file into a single entity again, just use the good old cat
cat xab >> xaa.(Do use ">>" as it append data from one file to another)