in reply to Fastest way of changing the beginning of a txt file..
Changing the front of a file is hard on most file systems, they just aren't built for this. Most DVRs use special file systems that allow for this, kind of like a doubly linked list. This way they can trim of the front of a file and alter the end as well, or keep a rolling 1 hr video file. There really is no quick way to do it safely other than choose a different file system.