On 4/28/05, Ian Trider <[EMAIL PROTECTED]> wrote: <snip/> > NTSC is analog -- the number of vertical scanlines is fixed at 525, of > which 486 are visible, or for convenience sake when dealing with > MPEG-type encoding algorithms (which work on blocks of 16) 480. > > Horizontal 'resolution' is dependant on a variety of factors; source, > method of transmission, receiving equipment, etc. You should be able > to capture (given that the capture card is of high quality) as much > detail as possible from the source (if it is a high-quality picture > from a local station received by antenna) with a resolution of > 540x480. If you are on cable, depending on the quality of your cable > system, 480x480 should capture full detail. > > Satellite is a different matter. Systems like Bell ExpressVu, > Starchoice, Dish and DirecTV are encoded already into MPEG-2 format, > usually at a resolution of 480x480 on the regular channels, at (IMO) a > far too low bitrate. However, because the receivers only have analog > outputs, that signal is converted back to analog NTSC and recaptured > by MythTV -- capturing at 480x480 probably won't quite capture the > entire resolution, but it's a lost cause, anyway. > > 352x480 will give you something approximately equivilent to a > excellent VHS recording at SP mode. > > Anythingx240 will be discarding have the scanlines vertically, and > will look terrible. > > Resolutiion does not affect file size, bitrate does. However, if you > reduce the resolution, the encoded image will be more similar to the > source in terms of artefacts. This is because there are fewer pixels > to be compressed into any given bitrate. > > Also a restriction you should note is that if you want to go to DVD > without reencoding, you are limited to the resolutions 352x240, > 352x480, 704x480 and 720x480. > > My personal opinion on the matter of 'what is acceptable quality': > > I capture everyday recordings at 352x480, with a bitrate of 3150kbps. > Some minor artefacts are visible in the image, comparable to satellite > (if you consider satellite quality to be acceptable, this bitrate > should be fine for you). > > My "high quality" setting is 720x480 (yes, this is overkill, but > necessary if you want to go to DVD) at a bitrate of IIRC 6200kbps. > This should yield an acceptable image, with almost no visible > artefacts when viewed on an SDTV. (think premium satellite channel). > > You might find this chart interesting: > http://www.mediachance.com/dvdlab/tutorial/bitrate.html > > .. though because the Hauppauge cards do not have the benefit of being > able to do 2-pass encoding (and the encoder, while good, is not the > best), you'll find that you'll need a slightly higher bitrate than the > chart indicates. For example, I consider 3150kbps to be on the low > end of good at 352x480 when encoded with the PVR-350).
Ian, thanks for the info! :) that's exactly what 'i' was looking for. i'm sure Jason and several others will also appreciate the quantitative data you've provided as well. thanks again. _______________________________________________ mythtv-users mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
