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| Digital Signal Quality http://forums.linhes.org/viewtopic.php?f=2&t=20460 |
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| Author: | johnlatz [ Sun Nov 01, 2009 6:16 pm ] |
| Post subject: | Digital Signal Quality |
Wondering if anyone can help me. I've been pulling out my hair, trying to figure out why digital recordings (both SD and HD) stutter and display visible compression artifacts. I've been digging through the nVidia drivers, the playback profiles, everything I can think of. Nothing seems to help. I'm wondering if there might be an issue with my recording? I play it back using VLC on my Mac and Windows laptops, and it doesn't look great there either. I use a high quality HD file (movie trailer) and it looks beautiful on my screen. Tried something new > mplayer -fs -zoom -vo xv -ss 00:00:00 /myth/tv/67985_20091031183000.mpg -display :0 Got the following output: Code: A:47454.0 V:47453.4 A-V: 0.638 ct: 0.034 1675/1580 22% 0% 0.8% 13 0
demux_mpg: 30000/1001fps NTSC content detected, switching framerate. Warning! FPS changed 47.952 -> 59.940 (-11.988010) [7] 0% 0.8% 13 0 A:47454.5 V:47454.6 A-V: -0.093 ct: 0.002 1705/1601 22% 0% 0.8% 13 0 demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate. A:47454.8 V:47454.8 A-V: -0.037 ct: -0.019 1715/1611 22% 0% 0.8% 13 0 demux_mpg: 30000/1001fps NTSC content detected, switching framerate. Warning! FPS changed 47.952 -> 59.940 (-11.988010) [7] 0% 0.8% 13 0 A:47454.9 V:47454.9 A-V: -0.020 ct: -0.028 1721/1616 22% 0% 0.8% 13 0 demux_mpg: 24000/1001fps progressive NTSC content detected, switching framerate. A:47455.2 V:47455.1 A-V: 0.017 ct: -0.024 1735/1629 22% 0% 0.8% 13 0 demux_mpg: 30000/1001fps NTSC content detected, switching framerate. Warning! FPS changed 47.952 -> 59.940 (-11.988010) [7] 0% 0.8% 13 0 Can't for the life of me think why the frame rate should be toggling between 48 and 60 Hz. Anyone got any ideas? |
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| Author: | mattbatt [ Sun Nov 01, 2009 10:56 pm ] |
| Post subject: | |
I was having a similar issue. I had transcoding turned on and the settings are really low. Also I'm assuming when you said playback profiles you meant Recording Profiles. My recording profiles defaulted to 480x480 changing that to 640x480 made a difference. |
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| Author: | johnlatz [ Mon Nov 02, 2009 7:44 am ] |
| Post subject: | |
This only happens on the digital side of my Hauppauge HVR-1600 card (so the recording should simply be the result of the card saving the digital stream straight to disk, no processing required - at least that's how I understand things). So there's no resolution change in the recording profiles, and I'm not transcoding afterwards either. I did mean Playback Profiles - my board has a nVidia GeForce 8200 video card, with which there seem to be known issues http://www.mythtv.org/wiki/NVidiaProprietaryDriver#Choppy_video.2FHigh_CPU_Usage. I was using the default playback profile (CPU++, "Standard" ffmpeg software decoding) and my CPU was spiking to 100% on one of the cores servicing Xorg. Found the posts on trying to set up nVidia cards with XvMC to avoid this problem http://knoppmyth.net/phpBB2/viewtopic.php?t=18456, but nothing I did with the Playback profiles helped the compression artificact problem I was having with digital recordings from my HVR-1600 (most every change I made to the playback profiles - including goign to XvMC made things worse). And like I said, pre-recorded movie trailers look brilliant. So I think I've convinced myself this must be a recording issue, rather than a playback issue. Currently on R5.5 (can't get R6 configured yet). MSI K9N2G NEO-FD nVidia GeForce 8200 AMD Athlon x2 5050e Hauppague HVR-1600 Thx Latz |
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| Author: | ceenvee703 [ Mon Nov 02, 2009 10:09 am ] |
| Post subject: | |
Is it equally bad on all channels that you've tried to record with the HVR-1600? Are you using an antenna or recording QAM off of a cable system? Have you tried to connect this source (either antenna or QAM cable) directly to your HDTV and see what kind of signal strength you're getting? I guess you could also try to tune to a channel via LiveTV and see what it reports the signal strength is, but I usually use my TV's signal strength meter. That "FPS changed 47.952 -> 59.940" line I think only means that it's detecting that the underlying thing you're recording is film (2x23.976 = 47.952). Here's another thread where someone had a different problem playing back and saw that same error line: http://mysettopbox.tv/phpBB2/viewtopic.php?p=120540 |
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| Author: | ceenvee703 [ Mon Nov 02, 2009 10:09 am ] |
| Post subject: | |
Is it equally bad on all channels that you've tried to record with the HVR-1600? Are you using an antenna or recording QAM off of a cable system? Have you tried to connect this source (either antenna or QAM cable) directly to your HDTV and see what kind of signal strength you're getting? I guess you could also try to tune to a channel via LiveTV and see what it reports the signal strength is, but I usually use my TV's signal strength meter. That "FPS changed 47.952 -> 59.940" line I think only means that it's detecting that the underlying thing you're recording is film (2x23.976 = 47.952). Here's another thread where someone had a different problem playing back and saw that same error line: http://mysettopbox.tv/phpBB2/viewtopic.php?p=120540 |
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| Author: | johnlatz [ Mon Nov 02, 2009 11:35 am ] |
| Post subject: | |
This glitch seems to affect all of my digital channels - the analog side of my card works just fine. I am a cheapskate - I pay Time Warner $18/month to get bare-bones cable: basic analog and unencrypted QAM (I'd be on an antenna, except I live behind two mountain ranges to the broadcast towers - if I don't get cable, I don't get TV). I titled this thread "Digital Signal Quality" because I've had trouble tuning in any channels using the basic source scan in R5.5 (it'll find some channels but not all the ones that Silicon Dust says I should have, and I can watch on my TV). I manually scanned for digital channels and found a lot more; I ran the azap program on a couple of the found channels, and after waiting a while to get a lock, it did seem to have a stable lock on the signal. But I didn't let it run for minutes on end - maybe I should. Also, I've got a lot of splits in my cable coming into the box. When I bought the house, I traced the line and found the previous owner had one 2-1 splitter in the line to feed the cable modem in the office and the TV in the living room. When I had my plasma hung on the wall, the installer split the cable in the living room once again: another 2-1 splitter to feed the TV and the PVR (using a single PVR-350 analog card at the time). When I got the HVR-1600 card, I found it requires separate inputs for digital and analog, so I had to split that leg once again to feed both sides. Analog doesn't look as great as it once did, but it is acceptable - and it works. Digital - I'm wondering if maybe the card is losing lock sporadically and causing the trouble? I want to dig into the wall and make the 2nd to last splitter a 3-1 to try to reduce any signal loss I might be experiencing (1 for the TV, one for the analog side, one for the digital side of my card). I'm no EE, but by my math that'd reduce power loss from 1/2 * 1/2 * 1/2 = 1/8th original signal strength to 1/2 * 1/3 = 1/6th original signal strength (yeah, I know db's don't work that way, but you get the gist). |
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| Author: | paulsid [ Mon Nov 02, 2009 12:03 pm ] |
| Post subject: | |
If signal strength is the problem you can buy a booster unit for around $20 at any electronics shop or department store. It's basically just a big splitter that plugs into a wall outlet. I have one that I used to use before I went to digital cable because I had to run about 4 different splits off one line and it works great... without it the cable picture was super fuzzy, but with it the picture was perfectly clear. BTW it's possible your issues are also related to ATSC support on the HVR-1600, as this is still fairly new. I've never used it on mine but I remember when I first got my card the ATSC was still on their TODO list. Presumably they've got it up to a reasonably stable state now, but that doesn't mean there aren't bugs... |
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| Author: | Liv2Cod [ Mon Nov 02, 2009 2:02 pm ] |
| Post subject: | |
I echo the advice about getting a booster amp. Try to place it as close to the incoming signal as possible, not at the end where your TV is. By boosting it ahead of the splitters you will achieve the best signal quality all along the chain. I want to point out that stutters can be caused by other factors too. My own digital programming stutters every time a network show comes back from commercial. At that time they usually have an overlay that shows upcoming shows or other trivial information. That overlay seems to cause a shift in the encoding rate, just as you have seen in your case. It goes away as soon as the overlay goes away, so I haven't pursued it further. |
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| Author: | johnlatz [ Mon Nov 02, 2009 2:34 pm ] |
| Post subject: | |
Thanks for the feedback, I'll look into a booster. As far as ATSC support on the HVR-1600, I recently reinstalled KM R5.5 and had to grab and install the latest cx18 drivers. From what I had been able to read, they've ironed out most all of the major bugs (but if you're better informed than I, please let me know). The HD clip that showed the stutters was actually an uninterrupted 1/2 broadcast on the local PBS affiliate - I'd like to claim I was smart enough to avoid the issue with coming back from commercial, but I'll take being lucky rather than good... |
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