WHY Won't MY DVR RECORD?

How/why did my DVR record the beginning of the movie when I pressed record after it had already started?

• This has happened to me twice recently: I turn on the TV and see there is a movie I'd like to record already in progress. I press record and then turn the TV off or switch to a different program. Then later, I return to my DVR to watch the movie, it turns out, the WHOLE movie is there, from the beginning and not from where I started the recording. What? Does anyone understand how or why this could happen? It has only happened with movies, not television shows, and it's not just like an extra minute added to the beginning. On one movie, I started recording 20 minutes after it had started; on the other, I started about an hour in. This is with RCN, on basic cable channels. Is this just a thing where the DVR is able to recognize the program is a movie and retrieve the entire thing somehow, regardless of when it was set to record? I mean, that's convenient for me, but I don't understand it! HOW DID MY DVR BECOME A TIME-TRAVELING MIND READER?!

• Answer:

  Short answer: the DVR is always recording when turned on. Cable DVRs start recording the tuned channel when switched on. They keep recording for two hours, then start dropping old data as more new data is recorded, so there is always a buffer of two hours. If you change the channel the process starts over again. The box doesn't care if the TV is on or not. So if the box is on channel Z, and you turn on the TV and see that there is a movie you want to record and press the record button, the data is already there if the movie started less than two hours prior. You are simply commanding the box to start keeping the data rather than discarding the data. The process *should* work exactly the same for any program, not just movies.