Improved CAM Handling

Discussion in 'support' started by mclog, February 13, 2007.

  1. mclog

    mclog Portal Member

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    Hi



    Basically, I love MediaPortal, everything works pretty well except for one thing, speed of Zap for encrypted channels. Non-encrypted for me is less than 1 second, encrypted about 9.

    As I understand it, every time you Zap the encrypted channels, MP is having to read the CAM details to decrypt the channels. Is it possible to hardcode these values somewhere in the source to improve the Zapping, and if yes, how do I do it :D

    Cheers

    McLog
     
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  3. jhb

    jhb Portal Pro

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    It isn't the reading of the CAM that is the bottleneck, it is the MPEG-coding of the channels. If you are zapping when a full frame just have passed, you have to wait for the next full frame before the channel can be decoded (which takes ut to a few seconds).

    And even if it was the reading of the CAM that was the bottle-neck, you can't hard-code it, you use a value from the signal to get the correct response via a crypto algorithm (many combinations are possible). Try un-plugging the card from the CAM and see how many seconds it is still working and you have the update frequency for your operator...
     
  4. mclog

    mclog Portal Member

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    How can other applications do it so much faster then? For example, MCE does it in about 1.5 - 2.0 seconds, DVBViewer the same, but MP is about 8 or 9 seconds.
     
  5. funkychicken

    funkychicken Portal Member

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    Because jhb is not that correct. I-Frames usually occur every 15-25 frames. These I Frames are what jhb calls the full frames. Since the MPEg system is capable of having more or less I-Frames every second, the GOP between different providers mpeg streams may be slightly different. Worst case though, it should take no longer than 2 seconds to receive an I-Frame. Given 2 seconds worst case to receive an I-Frame the rest of your 8-9 seconds is required to create graph/ decrypt stream / Check up database for EPG / start record buffer etc.

    Franky, MCE is far better at dealing with the processing of channel changes that MediaPortal.

    I use a technotrend DVB-S 1500 budget and exactly the same BDA drivers for MediaPortal and MCE. The difference is with MCE I use the TT AutoDecoder tool and channel changes occurs in 1-2 seconds with encrypted channels.

    Using MediaPortal on the same machine causes channels changes to take 4-5-6 seconds. I know the usual excuses, signal strength/quality etc but face it, MCE is better at changing channels than MediaPortal. It is the one reason I havent really commited to using MediaPortal yet :-(

    I have found that a virgin install of MP with NO epg/ no DVB-EPG grabbing / NO timeshift etc takes 3-4 seconds to change channels.

    I don't know how MP works internally but it sounds that the pipeline of actions during a channel change needs optimizing. i.e.

    Detect Channel change >> Change Channel >> Timeshift buffer >> Display channel guide etc.
     
  6. jhb

    jhb Portal Pro

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    Well I have around 1 to 2 s of switch time independent of whether I zap with my DVB-T box or my MediaPortal HTPC (FloppyDTV or Twinhan does not matter in most cases).

    With my Twinhan board zap time can sometimes be longer when I have poor reception, but I also have quality issues on those channels with that board...
    ...which was the reason that I got myself a FloppyDTV...
     
  7. mclog

    mclog Portal Member

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    I'm running FloppyDTV as well, switched from TT Budget, it hasn't made any difference to zap times.

    Interestingly though, when I can get TVEngine working, the zap times are much shorter, so obviously handled differently there. Only problem for me is getting TVServer stable :(

    Also, I notice that Frodo posted that he gets pretty short zap times with CAM decryption, so I'm wondering what he does that I'm not :)
     
  8. jhb

    jhb Portal Pro

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    New info

    After upgrading to the latest SVN (one week ago) I've gotten problems with slow channel switching and also notices that if I select to watch TV via the TV-Guide instead of selecting the channel directly I will have performance issues. It seems like the SVN from last week at least is very heavy on CPU usage, at least on my HW...
     
  9. jhb

    jhb Portal Pro

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    And after changing back to 0.2.2.0 stable release everything is back to normal. Fast channel changes and low CPU load.

    The only thing that made me leave that release (and now will continue to be a problem) is that the WebEPG is read in 12h wrong on some channels.
     
  10. jhb

    jhb Portal Pro

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    And latest SVN, 13331, works like a charm, many of my previous bugs have disappeared and I think channel zapping is even faster now.
     

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