Andy Walls wrote: > On Sat, 2009-11-28 at 10:31 -0500, Dale Pontius wrote: >> Devin Heitmueller wrote: >>> On Wed, Nov 25, 2009 at 12:59 PM, Dale Pontius <[email protected]> wrote: >>>> Using hvr-1600 capture cards on the NTSC side. All works well, but when >>>> playing back, or especially on live TV (In MythTV) the image centering >>>> is a bit off - down and to the right. In addition, the top line of the >>>> image is "itchy", flickering and so forth. >>>> >>>> Are there knobs somewhere to recenter the image? >>>> >>>> I presume the itchy top line has something to do with interlacing... >>>> It is present in MythTV, but disappears after transcoding. Is this >>>> something the right de-interlacer would fix? What should the >>>> de-interlacing situation be when I'm using NTSC TV-Out on the video card? >>>> >>>> Should this question really be asked on the MythTV list, also? I know >>>> the re-centering question is probably more appropriate here, and moving >>>> the image up might hide that top line, but perhaps the interlacing >>>> issues are better asked there. >>>> >>>> Thanks, >>>> Dale Pontius >>> I can comment better if you provide a screen capture of the issue. >>> However, it sounds like you are seeing the VBI information at the top >>> of the screen, which is usually hidden by a television's "overscan" >>> area. > > > Hi Dale, > >> I'll have to look into how to get a screenshot. I normally run >> fullscreen, which makes using screenshot tools (which I don't often do >> anyway) kind of tough to use. > > Could you tell me what your analog source is: broadcast cable, VCR, > Set-Top-Box, etc. and on what input: analog tuner, or SVideo or > Composite? > This is the analog tuner input, connected to broadcast cable. > >> But that's also why I was mention looking >> for a knob to recenter the image. > > "Knobs" to muck with HCENTER and VCENTER in the cx18 driver invariable > begin to affect capturing VBI data properly and maintaining HSYNC. > >> There's black to the left and top of >> the image, and it flows all the way to the right and bottom sides. >> Seems to me a little recentering plus a little overscan could take care >> of it just fine. But with the image shifted down as it is, enough >> overscan to take out the "itchy line" takes out too much else. > > Where is this itchy line? If it is in the Vertical Blanking interval it > should be mostly black with white flickering portions with the right > side of the line flickering more than the left. > Given what people have said here, I've looked again at the itchy line. It's not VBI. It appears to be an interlace problem, as best I can tell The top line of the picture appears to come and go, very quickly. It doesn't seem that fast, and I would swear I couldn't really see 1/30 second, but that's kind of what it seems like - the top line present on every other frame, going black on the alternate frames. There is no bright white coming and going - it's the image line flickering.
I'm guessing that someone's going to tell me to check my de-interlace option in MythTV. > The menu in MythTV has a "zoom" option IIRC correctly and it lets you > pan around the centering of the image with the arrows when enabled. > I recently fiddled with this just a little, while getting lirc working again after upgrading to 0.8.6. > >> Quantitatively, the down-right shift is on the order of the width of the >> typical single-height taskbar of the typical window manager. (In the >> current case, xfce - taskbar on top.) > > A full NTSC line is 286/4.5 MHz = 63.556 microseconds. Around 10.9 usec > are in horizontal blanking, leaving about 52.656 usec of active line > video. Sampled at the pixel clock of 13.5 Mpixels/sec * 52.656 usec = > 710 pixels. You can rely on about 3 pixel times being dark on both > sides of the line, so that means the visible, bright pixels on a NTSC > line is 704. > I've looked a little more at the centering. There is more space on the left, but still some space on the right. There is space at the top, but none on the bottom. > (That's of course if you told MythTV or mplayer to capture at 720x480) > > Get out a ruler and measure your screen. Knowing that the bright part > of a line is 704 pixels, you can estimate the pixel times that are dark > on the left and right side of the screen. > I'm set up for 720x480, since I was trying to set the capture native for the card. I have yet to do more of this - I just got my main backend machine up - it was offline while my daughter was home for Thanksgiving. She had a paper, and had her machine home with her. > > >> I'll find the time to look harder at the screenshot issue. When I've >> needed to do it before, I've used "xv" - I just don't do it often. > > I only have a STB to generate analog for me anymore. It's reconstructed > analog waveform is rather ideal. I'll still try to reproduce the > problem. > > But a window or screen shot would help. > > $ /usr/bin/mythfrontend -w --geometry 720x480 > > will open the Myth frontend in a window. > I'll give this a try - I didn't know you could put the whole thing in a window with a command line option like this. _______________________________________________ ivtv-users mailing list [email protected] http://ivtvdriver.org/mailman/listinfo/ivtv-users
