Explain this DVR space usage anomaly

I have a 100-hour DVR. It’s pretty consistent: one hour of programming is one percent usage.

But occasionally, something wacky happens, and a two hour program might use four or five. This morning I erased a 2½ hour program, and the space usage went down almost 10%.

What is the deal? I just don’t get it.

high def vs non high def programs?

Quality settings? Most advertised values (100 hour) are for their lowest quality setting. Perhaps your model of DVR is automatically recording certain shows (maybe HD movies or something) at a higher quality. My ancient 40-hour DVR is only an 11 hour DVR if I recorded everything at the highest quality.

If there is a power loss, mine defaults to the fastest speed.

Now that’s an interesing thought that I hadn’t considered, since I still have one of the old-timey tube TVs, and hi-def is lost on me.

Besides the SD/HD issue as mentioned above, not all channels are created, or transmitted equal. Service providers (Comcast etc.) usually recompress the data stream before sending it to customers, in order to get more channels out the door. So 1 hour of primetime network SD may contain double the data of 1 hour of off-peak not-very-popular cable channel.

When my kids were little, they watched a lot of a Noggin, which was a preschool age oriented channel of mostly animated shows. Comcast compressed the hell out of it. Artifacts all over the place. I could barely stand to watch it, but the shows took up almost no space in the DVR.

ETA: Who is your provider? Most of them these days transmit both SD & HD on different channels, usually differing by a constant offset. So channel 5 would be ABC SD, and channel 505 would be ABC HD. Or are you just using an antenna and grabbing OTA broadcasts?

unless the show is HD and you want to watch it in HD then don’t record it HD. you might have a number of choices for quality, maybe 4 to 6 quality settings. if you have a CRT set and used a quality VCR then the slowest speed may suit you fine.


I don’t know what equipment the OP is using but I have a Verizon FiOS rig, which doesn’t have any quality settings for DVR recording (and certainly not anything related to “speed”). It is recording SD or HD depending on what broadcast I select.

The OP does not have an HD set (well, at least that’s what I think when he says “old timey”) so would not have HD feeds into the DVR.

As far as compression, I would have expected that the DVR records the decompressed signal, the same signal that would go to the TV, but I really don’t know.

My DVR is a Magnavox, not provided by a cable company. It has various speeds and can dub between the harddisk and DVDs.
Yes, the ATT Uverse DVR has no selectable recording speed.

While I’ve got you here, a minor hijack.

The same U Verse programs are sometimes encrypted from being recorded to a DVD and sometimes not. They will dub to another harddrive, but not from the second harddrive to a DVD. What’s up with that?

Possible causes:

  1. As already mentioned, an SD vs HD signal.

  2. Some sort of variable setting on the device, perhaps choosing a better option based on type of content (i.e. movie vs sports vs TV show).

  3. The type of video, specially if the device is using some sort of variable bit rate encoding, can have an impact on the amount of space a recording will take up. An action heavy movie with lots of explosions and chases vs say a court room drama with long shots of the same frame, etc. Noise in the video can also have an impact in the space required. Film grain, artifacts, and other noise usually cost more in terms of bit rate to encode.

the content provider allows you (through the data sent) to time delay watch the show but not to archive it off the machine. that is what the content provider intends to do.

Sometimes the same program will not be protected.
I wonder if it is due to being compressed differently at different times of day.

Just because he doesn’t have an HD set, doesn’t mean he doesn’t have access to HD channels. We don’t know if he’s got a service provider, or recording OTA. The data coming into the DVR is all over the same device (antenna, cable, or fiber), and the HD channels are there, even if he can’t watch them. And I believe most or all service providers now only offer HD-capable DVR boxes, so he may be accidently recording HD channels.

DVRs all record the already compressed MPEG-2 or MPEG-4 signal. Recording an uncompressed signal would take 5-10 times as much storage space.

I don’t see why. The compression or lack there of of the signal has little to do with the compression being used by the recording device (aside from the issues I mentioned above).

It’s still taking a particular frame size, breaking it down to blocks and compressing/encoding. Doesn’t matter if the image is pristine 4K content or one of those terrible commercials on cable TV that appear to be heavily compressed you-tube videos (aside from the frame size of course!).

All incoming digital signals are already compressed to MPEG-2 or MPEG-4. Those are the standard video compression algorithms in use for OTA and all cable broadcast, and I think satellite as well.

The absolute easiest thing for a DVR to do is to tune, then just write that compressed data straight to disk. Very little processing required. Then, during playback, just decompress it and put it on the HDMI/component/whatever outputs.

Tune->Decompress->recompress->disk requires extra hardware and processing capability for the recompression step. Would also require multiple decompression hardware if it’s a multiple-recording DVR. While decompress-on-playback only requires a single decompression to ever happen at one time.

Tune->Decompress->disk would require much larger disks for a given recording capacity, and still has the multiple-decompression hardware issue.

Cable companies are nothing if not cheap, so they all just write the MPEG stream straight to disk (actually, then encrypt it first). I guess there may be some OTA DVRs that decompress a digital broadcast then recompress and write to disk, but I’m not aware of any.

I guess if any cable companies are still delivering analog signals and using DVRs that have to encode/compress on the fly, you could have some kind of quality setting.

Hmmm, I didn’t know that’s how the cable company DVR’s worked. I use an HTPC so it’s always decrompress -> compress - > disc for me.

Would a DVR setting of 480i vs. 1080i affect recording or is that simply playback?

Yeah, I bet you play PC games instead of console games like God & George Washington intended.

Seriously though, what’s your signal source? encode/decode hardware? Is the HTPC market still mostly build-your-own? I’d guess in that space, there’s a market for variable compression capabilities.

That’s simply an output to TV setting.

Yeah I play PC games, like YHWH intended :cool:

I’m running an AMD A8 based system for my HTPC setup. I have a Ceton Infinity TV tuner which supports the dreaded cable card so I can tune in to the HDTV channels because the FCC refuses to light a candle under the cable companies behinds to get more modern and HTPC friendly alternatives out. And yeah, I believe it’s still mostly do it yourself outside of a few companies who will sell you overpriced monstrosities.