Hmmm, OK now I'm a bit better off on the dark scenes. I set it to record by default as: 320x256 mpeg4, bitrate = 2200 (scaled from 640x480)
with the interlaced and high performance settings turned on (I've got a 1.6 P4 so I figure I have the processor to burn). I've noticed a few things from these settings and from watching this discussion. First of all while the dark scenes are definitely better I notice that when the scene is moving fast I now get interlaced type lines showing up. Am I correct in assuming then that I should not be selecting interlaced because my card is only able to capture at 240 lines so its actually only capturing every other line anyways? Incidentally my card is a bt878 variant I believe (I may upgrade to a PVR250 at some point but not right now). Is there any point for me to do a higher resolution on this card? Paul On Mon, 2005-02-07 at 08:38 -0500, Cory Papenfuss wrote: > > It most definitely is not. I don't have any links on hand, but > > vertical resolution (because of how the signal is transmitted -- the > > analog signal is a continous wave with points at regular intervals at > > certain points marking the point where fields begin/end) is ALWAYS > > bang-on 480 regardless of source. > > > > Horizontal resolution is variable (for the aforementioned reason), but > > (assuming your capture card doesn't suck; bt878's do) in theory, > > 352x480 (on a good card) is enough for VHS and ~540x480 (on a good > > card) is enough for broadcast. > > > > If the source is from a digital source, such as satellite -- Dish, > > DirecTV, Starchoice and ExpressVu all transmit a signal at 480x480. > > There will be some lossage of course, in the A>D>A>D process that > > occurs when you capture the output. > > > > However, if you are viewing on a PC, and the deinterlace filter is not > > very good (i.e. it drops a field to deinterlace), there MAY NOT be a > > visible difference between 240 and 480 vertically. > > > > Certainly you will see it on a TV. > > > > (Nevermind the MythTV FAQ, the bits about capture size are not > > entirely accurate) > > > Well said. It's amazing how many people are confused as to the > real meaning behind "capture resoltion." Much of it comes from the term > "lines of resolution" which is a term from long before digital video. It > describes how many lines can be resolved on the continuous (analog) > horizontal scan you described. So, *vertical* lines are drawn on the > screen closer and closer together until they blur together. These lines > are counted across a width of screen equal to the height. For a 4:3 > aspect ratio then, the "240 lines" for VHS equate to 240*4/3 resolvable > dots across the screen, or roughly 352x480. For broadcast, the "80 > lines/MHz" rule of thumb and , 4.2MHz luminance cutoff equate to 330 > lines. That's 330*4/3, or roughly 480x480 for broadcast. This whole mess > is also why a DVD is described as 540 "lines of resolution"... since if > you draw a 4:3 picture with 720 horizontal dots, you only count 3/4 of > them since "lines" is defined as per-picture height. > > There... I feel better. Bottom line is the number of scanlines is > *FIXED* by the TV standard (visible NTSC 486, PAL 576). The number of > dots to cut up the horizontal scan is somewhat arbitrary, but that's what > "lines of resolution" refer to. It pains me to hear people talking about > capturing TV at 320x240 since it's 1:1 square pixels, and "there's only > 240 lines of resolution anyway." Tragic... :) > > -Cory > > > > ************************************************************************* > * Cory Papenfuss * > * Electrical Engineering candidate Ph.D. graduate student * > * Virginia Polytechnic Institute and State University * > ************************************************************************* > > _______________________________________________ > mythtv-users mailing list > [email protected] > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users -- Paul Gratz <[EMAIL PROTECTED]>
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