Once upon a time hawkins1of3 shaped the electrons to say... > using 2.20 GBs of space. A 1 hour show in best quality on Digital > cable is 1.50 GBs of space. A show I record on basic cable that is > only high quality is 1.50 GB of space as well..
Size will vary by show, even on the same source. MPEG-2 encoding is largely a differential system. Key frames are encoded in full, but then the following frames are only the differences from the key frame, until the next key frame. Shows that have a lot of motion, rapid camera changes, even a lot of colors, create more differences frame to frame, and hence more data to encode. Shows that are full of static shows, fewer colors (lots of dark scenes), or little motion compress much more readily. So you can't really compare two different shows. The only really accurate test would be to record the same episode of the same show - one from the cable box, and one from the analog tuners. You could do this with a cable show that airs repeatedly by going into your Channels list and forcing a channel to the box and then the internal tuner, respectively. That will give you an apples to apples comparison. > So I guess there are multiple questions I have.. First would be > whether anyone knows why it uses less space, and second if it means it > is lower quality, and third is whether that means I can hold more > shows on my HD if I only recorded in digital since I am using less > space per show in digital? 1. Well, as I said above, encoding will vary show to show, so until you have an apples to apples comparison you can't be sure it is really saving anything significant. However, presuming it *is*, there are a couple of possible reasons. First, it is possible that your cable company does digital simulcast. That's where an 'analog' channels is also broadcast in the digital spectrum. Analog tuners (like the one in the TiVo) use the analog signal, but cable boxes (and CableCARD tuners, like the Series3) can use the digital signal. The digital signal is generally cleaner than the analog signal. So the cable box tunes a better signal with a clearer image, and, especially if you're using S-Video, feeds this to the TiVo to encode. This image has less noise than the analog image. The encoder doesn't know noise from real image data, so it has to encode everything. Noise - fuzz, static, etc - creates differences frame to frame, which get encoded as image data. Take the same image, one with noise and one without, and the one without needs less data to store the encoded version. Another possibility is that the cable box is tuning the same analog source, but it has a better tuner and/or does some kind of noise filtering or image smoothing on the image before sending it to the TiVo - resulting in the same thing, a less noisy signal to encode. Note, if you're doing apples to oranges comparisons (two different programs recorded) and one is from the internal tuner (analog) and one is from a digital cable station (box) then the analog/digital difference (noise) is probably the answer - along with differences in the source. But if you record an analog show via the cable box (which you have to force - by default the S2DT always uses the internal tuner for analog) it may not save any space over the internal tuner - and may even use more space. That's why I say do an apples to apples comparison. 2. No, a smaller size doesn't necessarily mean lower quality. Given *identical* image sources, with the same encoder, a smaller file size DOES indicate a more lossy encoding, which generally means a lower quality reproduction when decoded. Hence Basic looks worse than Best. However, given the same encoder, with the same settings (both recordings are Best), if one recording is smaller than the other, it is most likely a difference in the source material. One program had more data to encode than the other. 3. Given apples to apples, if the cable box recordings take up less space than the internal recordings, then sure, using the box will allow you to store more. But, odds are, the same analog content recorded via the internal tuner or the box will use the same amount of space. And using the box loses the dual-tuner aspect. Using the box also may lower the image quality - with the intenral tuner the channel is tuned and fed directly to the encoder. With the box it is tuned, modulated for the appropriate output, then fed over an analog link to the TiVo, where it is captured, then fed to the encoder. There are many variables. -MZ -- megazone-at-megazone.org http://www.MegaZone.org/ Gweep, Geek, Human, me. http://www.TiVoLovers.com/ http://www.Eyrie-Productions.com/ -><- Hail Eris "A little nonsense now and then, is relished by the wisest men" 508-852-2171
