Hi: I'm not an expert here, but if you're using software encoding (e.g., compression), I think the noise is your problem. Video compression generally works by taking a starting frame, then saving the differences from one frame to the next for a few frames, then including a new complete frame, etc. In MPEG, the full frames are called I-frames and the difference frames are called P-frames (if my memory is correct; its been a while since I've read up on this).
Now noise is generally random. This means that each frame is going to be a fair bit different from the last just due to the noise. Since each frame has more differences, the P-frames are bigger (assuming the bitrate is not constrained; if it is (like the PVR series does), then you'll see an increase in mpeg artifacts and other signs of poor encoding or insufficient bitrate). This will result in larger recordings. If I recall correctly, this was a major consern of the digital sat providers in the early days; they went through great lengths to clean up analog video before encoding it in an attempt to get better compression. I would strongly recommend contacting Comcast and placing a trouble call. They're supposed to proide clear pictures on all channels, even in analog, and will often do this at their expense. I know out here they were very responsive when I called up with signal problems after adding another capture card (and splitter). Alternatively, you can see if you can constrain the bitrate on your encoder/transcoder settings. --Jim Phil Buescher wrote: >I've been running Myth for a couple years now. I'm just running it >with a software based encoder Happauge WinTV-Radio. > >I moved to a new town just recently, and a different cable company, of >course - I have Comcast now. >Anyway, onto the problem... > >Certain channels come in pretty fuzzy, with bad quality, showing >diagonal lines on the screen. Most channels come in just fine and >look great. These channels come in all fuzzy on a normal TV as well. > >Here's the big problem though - on those channels with the poor >quality, the recording sizes are abnormally HUGE! >We're talking about 3-4 times larger than the recordings should be. >For instance, a normal hour-long show will take up 0.74 gigs, but the >ones on the flaky channels will take up anywhere from 2.5 to 3.5 gigs! > It's really crazy! > >I didn't change anything besides my tvlisting feeds on my MythTV box, >so I know it isn't something I did. I didn't change my recording >format, I didn't change my setup, and this is certainly a per-channel >problem. Only two channels I know of have this poor quality and HUGE >recordings problem. > >I did get basic cable, nothing digital, no satellite or anything goofy >- just the basic standard cable package with no need for a set top >box. > >Could this be that these channels are actually HDTV, and that's why >they're taking up so much room and come in all fuzzy on tuners that >aren't HDTV-ready? Or can it just be that channels with this poor >quality problem simply take up a ton more room to record? I have DSL, >but could I be receiving some interferance that has to do with cable >Internet? I don't know - I'm totally guessing because I have no clue >anymore. > >I really need some help, as the two channels we record the most shows >off (shows that are on while we're at work), are the ones that have >this problem - and even with over 300 gigs of HD space, I'm running >out rather fast. > >I really don't want to have to re-transcode/mencode the shows after >recording them, since that's a pain - any idea what the problem is? >The cable installer thought the poor quality was due to bad wiring, >but between him and I, we replaced every single run of cable in and >outside of the house with high-quality wiring and ends. The installer >even replaced the cable running from the neighborhood box that runs to >our house. We never did figure out why these channels come in fuzzy. >He left, proclaiming the problem fixed - and it wasn't fixed, he just >checked one of the channels that come in just fine. I even bought an >expensive coax tester, and all the runs are totally clean. > >I tried putting a signal booster in front of my MythTV box, but that >had no effect. I also tried an RF filter, to no effect. I'm totally >stumped and frustrated. > >Please help - any suggestions or insights are appreciated. >_______________________________________________ >mythtv-users mailing list >[email protected] >http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users > > _______________________________________________ mythtv-users mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
