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"Heroes" Playback judder
http://forums.linhes.org/viewtopic.php?f=17&t=15227		 Page 1 of 1
Author:  acronce [ Mon May 14, 2007 10:05 pm ]
Post subject:  "Heroes" Playback judder
Hi all,

I've found that recent recordings of "Heroes" have considerable judder during playback. For example, if a person moves across the screen, there is a slight, intermittent hesitation. My wife doesn't see it, but it's very noticeable to me.

I don't see the problem on any other HD recordings. And it is not present in Heroes recordings from earlier in the series. It's something that has started happening since the show came back from its break.

I'm running the Mac OS X MythFrontend with a R5E50 backend. The problem is visible and consistent on all machines I've tried.

I ran the frontend in verbose mode and found the following oddities in the logged output:

Code:
2007-05-14 20:40:51.165 NVP: Video is 3.1346 frames ahead of audio,
                        doubling video frame interval to slow down.
2007-05-14 20:40:51.231 NVP: Video is 3.22757 frames ahead of audio,
                        doubling video frame interval to slow down.
2007-05-14 20:40:51.298 NVP: Video is 3.16993 frames ahead of audio,
                        doubling video frame interval to slow down.

There's tons of these entries indicating that the video is being slowed down because it's ahead of the audio.

I don't know if this is related, but intermixed with the above audio slow down warnings are a bunch of interlace related warnings:

Code:
2007-05-14 20:41:01.774 NVP: interlaced frame seen after 5 progressive frames
2007-05-14 20:41:01.847 Enabled deinterlacing
2007-05-14 20:41:01.921 NVP: progressive frame seen after 4 interlaced  frames
2007-05-14 20:41:01.994 Disabled deinterlacing
'video_output' mean = '37363.86', std. dev. = '8055.00', fps = '26.76'

Note that I've always noticed interlacing problems on Heroes, especially during scene changes. So maybe this has something to do with the source material.

Anyway, the end result is that this show is barely watchable through Myth. But if I watch it via my Mits built-in receiver, it looks flawless.

If anyone has suggestions as to what I can do to improve the playback quality of this show, I'd appreciate it.
Author:  manicmike [ Mon May 14, 2007 11:21 pm ]
Post subject:  Re: "Heroes" Playback judder
acronce wrote:
Hi all,

I've found that recent recordings of "Heroes" have considerable judder during playback. For example, if a person moves across the screen, there is a slight, intermittent hesitation. My wife doesn't see it, but it's very noticeable to me.
--snip--
If anyone has suggestions as to what I can do to improve the playback quality of this show, I'd appreciate it.

Hi,

Some info from wikipedia http://en.wikipedia.org/wiki/High-definition_television
Quote:
In general, 720p is more appropriate for fast action as it uses progressive scan frames, as opposed to 1080i which uses interlaced fields and thus can have a degradation of image quality with fast motion.

In addition, 720p is used more often with Internet distribution of HD video, as all computer monitors are progressive, and most graphics cards do a poor job of de-interlacing video in real time. 720p Video also has lower storage and decoding requirements than 1080i or 1080p.


Is it broadcast as 720p or 1080i? If the former, the problem is likely to be that you're deinterlacing a non-interlaced signal since you'd be experiencing the video card deinterlacing problem above. You should be able to discover in which format the show is broadcast (look at the mythbackend log file). If it's actually broadcast in 720p turn deinterlacing off and the problem should be gone. If it's broadcast in 1080i, your hardware (and being a mac this seems incredibly unlikely) could be not up to the job.

Great show, so I'd also spend time getting it right 8)
Author:  ceenvee703 [ Tue May 15, 2007 2:53 am ]
Post subject: 
Heroes is an NBC show, and NBC broadcasts in 1080i. My guess is that the Mac can't keep up with doing the deinterlacing of the signal. Which Mac are you using for a frontend? Some have pretty weak graphics cards (and I don't know if the Mac versions of Myth have gotten XvMC working).

Also, I think that MythTV recognizes whether the recording is 720p or 1080i and doesn't try to deinterlace the 720p recording. So you don't have to manually turn deinterlacing on and off, it should be doing it for you.

EDIT: this page has some discussion that might be applicable:

http://www.mythtv.org/wiki/index.php/Ta ... on_Mac_x86
Author:  acronce [ Tue May 15, 2007 9:22 am ]
Post subject: 
Thanks for getting back to me. I mostly watch Myth via a dual 1.6 Ghz Intel Mini hooked at 720p to my TV. I agree that the Mini has lousy onboard graphics. But I also see the same problem on a top of the line 2.33 GHz Core 2 Duo Macbook Pro with a built in Radeon X1600 with 256 MB of VRAM.

I used to run the Mini at 1080i because that was the only input option with my older HD TV. I had all sorts of problems getting 1080i source material to display properly without dropped frames. Ultimately I had to hack the source code to fix what I found to be scaling bugs. Here's the gory details if you're interested:

http://mysettopbox.tv/phpBB2/viewtopic. ... highlight=

But a few months ago my TV died and I got a new Mitsubishi 1080p unit. Originally I drove it at 1080p using my hacked version of the MythFrontend. But ultimately I found that the Mini had fewer distracting interlace and tearing artifacts at 720p, especially with fast action scene changes. So now I'm running the stock, non-hacked MythFrontend at 720p.

Based on my experiences so far, this problem doesn't seem to be performance related. I watch all sorts of other 1080i material at 720p on the Mini with much more reasonable results.

Based on the log entries, it seems to me that there's something specific about the Heroes source material that is at the root of the problem. And it's something that's changed pretty recently, because I have some saved older episodes from before the season break that do not exhibit the problem.

If anyone has further suggestions, I'd be interested. Maybe when I have more time this weekend, I can poke around with the source and see if I can determine what's really happening here.
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