[mythtv-users] Channels with poor quality create HUGE recordings

Sat Apr 16 00:51:20 UTC 2005

Wanted to post the resolution, even though it's a strange one.

I have no explination for why this fixed it, but here goes...

First I tried the software-based video filters from within the channel
editor, as suggested.  However the option that was suggested,
"quickdnr" just crashed mythbackend whenever I tried to view that
channel.  So I tried "linearblend,denoise3d=12", and that actually
seemed to help things quite a bit.  The record size was much smaller
(I watched this by comparing how fast my buffer filled while paused),
but still larger than normal, and the quality was still very poor with
diagonal lines.

I then put on an FM filter, to see if that would help clear things up.
 It didn't seem to help - in fact, it seemed a little worse.

So for lack of anything else to try, I pulled off the FM filter and
put on a signal booster, and that didn't help either, again, making it
seemingly worse.

So just for giggles I decided to put on both the signal booster, and
the FM filter as well.  Imagine my amazed surprise when my picture
quality was near PERFECT!  I mean, it looks just like any other
channel, with very clear nice quality.
And my recording size is totally great!  Completely normal sized recordings.

Now, the FM filter probably didn't do crap, because there's no reason
I should be getting FM interference.  And as far as the signal booster
goes - both my cable installer and the guy at radio shack told me it
wouldn't do anything for me.  The software video filters seemed to
help some, but certainly didn't make the end result happen.

I had to use all three to get a clear picture quality.

Well, I'll let you all wonder just why that's the case, because I have
no friggin' clue.  I guess something about boosting the signal, then
filtering it, and finally running some software video filters on it
made my picture quality totally crystal clear.  Or at least as clear
as standard cable gets.

Oh well, I'm totally happy now.  Thanks all for the info - I know a
lot more about cable than I did before now.
Still - I wonder if tweaking the software video filter's parameters if
that would have fixed it by itself?  Who cares, I'm not touching a
darn thing - it works.

Now then, I'm off to delete some horribly huge records and schedule
re-recordings of them, now that they'll be clear.

On 4/14/05, Jim Kusznir <jim at kusznir.net> wrote:
> 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.
> >_______________________________________________
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> >mythtv-users at mythtv.org
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> >
> >
> 
>