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Thread: PCH video problem with UK HD channels

  1. #1
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    PCH video problem with UK HD channels

    I get video rendering problems watching HD recordings on my PCH. SD recordings are always fine.
    It looks like pixellated MPEG blocks especially on the right hand side of the screen are not being updated fast enough. This doesn't happen all the time, and only on some recordings. In summary I believe it is caused by UK Freeview switching between 1080i and 1080p, but I don't understand why I seem to be the only one with the problem!

    I am running a PCH A-110 with no internal drive and with a wired network connection to NPVR running on a 64-bit machine with hardware RAID 5 disks and am running the latest versions of all firmware and software. I am recording UK Freeview from a Blackgold BGT3620 dual DVB-T/T2 card.

    When Freeview HD first started up in my region last April I only had the problem on BBC HD but sometime in the summer it spread to the other 3 HD channels too. I have given it a good deal of thought and done a few tests to try and isolate the problem so I believe it is none of the following:

    It is not a bandwidth problem. I can watch blu-ray rips as .mkv or .ts at full bandwidth without any problems.

    The problem is not in the recording. The recordings play back fine on my PC using VLC or Power DVD 8.

    It is not an HDMI problem. You can see the same pixellation problems on the analogue output from the PCH.

    It is not an NPVR problem. You get the same problem playing back files directly on the PCH over the network.

    Changing PCH video sync options doesn't make any difference.

    An important observation:
    It is temporarily fixed by doing an NPVR skip backwards. If you skip backwards by a few seconds the PCH successfully replays a piece of video that was being pixellated absolutely fine. I have set the short backwards skip in NPVR to 1 second so I can get rid of pixellation while I am watching, but it often soon comes back a little further on. It is as though the skip backwards brings the renderer back into sync somehow. Pausing and restarting doesn't have the same effect and the pixellation continues.

    I think it is a problem caused by UK Freeview switching between 1080i and 1080p. The problem seems to be associated with times where video switches from 1080i to 1080p and back, this happens a lot in programme title sequences and any video FX sequences, and places where there are edits between studio and OB clips. Some programmes are fine after titles e.g. Later with Jools Holland (the 5.1 audio here is excellent by the way). Here is a link describing the Progressive/Interlace switching that happens on UK Freeview these days: AVFORUMS 1080i/1080p.

    Here is what you get in the Handbrake log if you run one of the recordings which shows the problem through it and e.g. convert it to an mkv file:
    Handbrake log example:
    [08:58:19] 21.052278s: Video -> Film
    [08:59:00] 58.012278s: Film -> Video
    [08:59:25] 78.772278s: Video -> Film
    [08:59:41] 92.012278s: Film -> Video
    [09:01:18] 170.132278s: Video -> Film
    [09:01:30] 183.012278s: Film -> Video

    I am assuming that handbrake means Interlaced by "Video" and Progressive by "Film". NB after conversion by Handbrake to mkv it plays fine.

    So, has anyone else seen this problem, or any suggestions? I am beginning to think the PCH hardware may be at fault, perhaps I should get another one?

  2. #2
    Join Date
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    When I read the post on avsforum I started a post http://forums.gbpvr.com/showthread.p...9-BBC-HD-1080p and got a sample and I noticed some minor problems which I considered bandwidth related but I could never isolate them or figure out any good solution. If you want to upload some 200MB samples which show the problem to megaupload it might add to my body of knowledge, but I can`t say I will have solution. I suspect it is a demux problem and unlikely that it is a problem with your NMT.

    Martin

  3. #3
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    Sorry I missed your earlier thread. The sample uploaded by ACTCMS in that thread - http://www.megaupload.com/?d=PLUX2BN7 is a perfect example of my problem. The sparkly blue door is there all right, but is not what I am focussed on.

    At about 85 secs into the clip it switches from 1080i to 1080p just where the closeup of the envelope happens. The bit rate jumps here from about 6.5Mbps to over 10Mbps. At this point the video from my A-110 starts breaking up all over the screen and remains like that until the end of the clip. However, if I do a 1 second backskip during this section the video returns to normal until the end. If I am playing the file back directly on the PCH without using NPVR I can play the last section back fine by dropping straight into it using the 7 for 70% button, as long as that transition is not included.

    I don't have a hard disk in the PCH to try local playback from, but I got exactly the same result by playing the clip back from a USB stick plugged directly into the PCH. The transition from i to p seems to wreck the PCH's rendering, maybe by messing up its video buffering strategy?

    I am hoping that others don't see this problem so that I can fix it by swapping the PCH hardware!

  4. #4
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    As I said I think that is the NMT itself, I have more than one player and they all do that. Players with newer Sigma chips can handle it but unfortunately I don't have enough access to this kind of material to see if there is anything I can do about it. I do suspect a short skip would fix transitions. I didn't focus on the door either, I just don't feel it is a great recording for the PC or NMT and I think BBC viewers should react a bit to the quality they get.

    Martin

  5. #5
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    Thanks for your help on that Martin. I guess if I can't reliably play back UK Freeview HD material on my A-110 I could still use it for the NPVR interface, and for most playback.

    I really want to be able to play back these HD recordings without video artifacts and with 5.1 sound. Do you know if any of the later PCH boxes, especially the Popbox V8, would play the HE-AAC 5.1 audio decoded to PCM over the HDMI connection. It's not made clear anywhere, and stereo downmix is mentioned which I really don't want.

  6. #6
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    I really don't know what your extender options are for HE-AAC 5.1 output, it's not something I concern myself with. Most extenders and AVR's were designed for BluRay/DVD playback and using more traditional audio sources or direct connection to HDMI monitors that only want two channels. Pass through of HE-AAC is probably not an option and AAC pass through is limited to a few AVR's.

    If you can remux the HE-AAC to AAC (or even AC3) and then make an mkv or mp4 you probably would have the best change of portability.

    Martin

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