Yes you will have null video files.
Zero bytes still takes up space, if you look at them in the file explorer the size doesn't change, since 00 bytes are repeated all until the end of the file, lossless data compression algorithms takes good use of repeated bytes, hence the compressed file is so small.
i think that's how it works
though i am not sure.
OR
you can take srep for example, it just saves the position of dupes occurrence and copies a single of copy of these dupes to those positions during decompression.