Changing bitrate & resolution (Mode 0)

Discussion in 'TiVo Series 1 - UK' started by sanderton, Aug 21, 2003.

  1. Aug 21, 2003 #1 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    I know you can change the bitrate and resolution used by the MPEG chip on US stanadalone Series 1s.

    Has anyone tried this with a UK machine?

    The resolution settings for US machines are well understood, but do we know what the numbers are for ours?
     
  2. Aug 21, 2003 #2 of 529
    Sneals2000

    Sneals2000 New Member

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    I was interested in this as well - as I find the horizontal subsampling the most annoying thing about Tivo (especially the chroma) However ISTR that whilst people have had a good level of success modifying US Tivos to run at 720 samples horizontally, when this was tried on UK models there were problems with positioning and green bands appearing to one side of the picture?

    I think that people HAVE managed to improve the picture quality at the standard resolutions by increasing the bit rate though.
     
  3. Aug 21, 2003 #3 of 529
    mrtickle

    mrtickle Active Member

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    I did a lot of experimenting with this last week as it happens! Knowing that I was going to replace the drive I had nothing to lose!

    Assuming you have tivoweb of course and know how to use the resource editor (press return to submit each and every change you make; select the "update resources" link after doing them all). I measured these resolutions (*):

    0 = 720x576
    4 = 544x576 "best"
    2 = 480x576 "high"
    1 = 352x576 "basic"/"medium"

    Selecting resolution "0" (I modified my "high" setting as I don't use it much) did have the problems you mentioned. Basically the picture is offset to the left quite a bit and up a little bit. But the increase in resolution was certainly noticeable.

    The other main thing I noticed was that we don't have VBR. Even with "save disc space" turned on, tivo still doesn't use VBR mode. I'm suspicious that this is because both the "DBSBestVBRBitrate" and "DBSBestMAXBitrate" are set to the exact same value (for example Best quality with Sky digital lineup). When you start a recording the tvlog says "using CBR, bitRate=5960000, maxBitrate=5960000" nomatter whether you have Save Disc Space on or off. If you then set the VBRBitrate to a different (lower) value, tivo reports that it is using VBR mode in the logs.

    I also changed the live buffer to Medium :)

    There is also this thread:
    http://www.tivocommunity.com/tivo-vb/showthread.php?s=&threadid=108462&highlight=bitrate

    I set my "Basic" to 800000 and 850000 values (NB: this made it use VBR mode, even in Basic!). It looked fantasically awful - like old AVI files where the colour disappears and you get blotches of grey. It also made the tivo say I had 314 hours of Basic quality on my 138GB drive.

    HTH
     
  4. Aug 21, 2003 #4 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    Interesting; I will have a play.

    If VBR is not set up right (It's the AltBitrate settings for VBR mode isn't it?) then are those who report lower quality suffering from a placebo affect?

    (Personally I've never been able to tell the difference so I feel vindicated!)

    I only use Basic for Radio, so will se how low you can go!
     
  5. Aug 21, 2003 #5 of 529
    mrtickle

    mrtickle Active Member

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    To answer the question - dunno :)

    But I don't think that the AltBitrate page controls VBR. You'll see two values for each quality setting - I think the one with "VBR" in it controls VBR.

    My suspicion is that the Alt page is for the 2nd tuner on DirecTivos. Annoyingly, all guides seem to say "change them all just in case" without any more discussion :(

    On my machine I didn't touch the Alt page - and I only edited the DBS values on the main Bitrates page. This was after trial and error of setting all 6 possibilites (DBS, CAT, Roof in Bit and Alt) to slightly different values and seeing which values made it into the logfile!)

    Indeed. I set Best from 5960000, 5960000 to 5660000, 5960000. This made it start to use VBR. An hour of Best went from 2580MB down to 1800MB (reported sizes from tivoweb) and I couldn't really tell unless I looked very hard that it was different.

    Yes that was the idea of the chap on the other thread :). I noticed that even on the Sky digibox radio screens, where the only thing that changes is the time - once a minute - it takes a very long time to settle down to a clear image!
     
  6. Aug 21, 2003 #6 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    OK, I've done a bit of fiddling!

    Here are some stills of the results .

    They are quite large, I'm afraid; the page is ~2Mb.

    Here are the Sky red dots in the two resolutions:

    [​IMG] [​IMG]

    To do this I reset Medium resolution to be resolution = 0 and upped its bitrarte to 7000000.

    Although the screengrabs show a green area on the right, it does not appear on my TV. I see a perfectly normal looking picture. It seems from comparing the captions that there is a slight left shift - but it's not noticeable unless you are looking for it.

    You can also see from the artifacting on the caption that the bitrate increase has had a noticeable effect.

    The "real" resolutions of the two (ie, the picture area, not black or green bars) are 533 x 568 in Best and 677 x 568 in my edited Medium, so the resolution increase is real!

    I may have to lash out on another 120Gb drive to allow me to up the bitrate and res!
     
  7. Aug 21, 2003 #7 of 529
    mrtickle

    mrtickle Active Member

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    Cool, glad you got it working! I can only just see the green bar on my TV too - although I do have the overscan reduced to minimum.
     
  8. Aug 22, 2003 #8 of 529
    Brownedger

    Brownedger New Member

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    Stoke on...
    Are you saying that VBR doesn't actually work on the normal Tivo's or just the upgraded Turbonet Tivo's?
     
  9. Aug 22, 2003 #9 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    All TiVos.
     
  10. Aug 22, 2003 #10 of 529
    Brownedger

    Brownedger New Member

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    Stoke on...
    Ok is it working in the latest American release ver.3.0?
     
  11. Aug 22, 2003 #11 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    I assume so. To be honest it looks like a mistake by the people rolling out the UK version - the configuartion file variables just look like they are set wrong, with the max and min bitrate set to be the same!

    I'm going to try boosting Best by leaving the minimum at the current CBR level but giving it the option of adding maybe 1Mbps at peaks to see if that helps it with fast moving sports.
     
  12. Aug 23, 2003 #12 of 529
    NickDvl

    NickDvl New Member

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    For us lesser mortals, how many hours of recording time can you get out of those higher bitrate/resolution settings on a 120GB drive? Are there any other side-effects besides the green strip on the right? Do the settings survive a reboot?

    I've always found the horizontal resolution somewhat lacking on widescreen broadcasts, would be great if it could be improved... :)
     
  13. Aug 23, 2003 #13 of 529
    LJ

    LJ New Member

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    Is there a list of the resolution modes somewhere? Is there a mode 3? ;) I tried a search of the forums and read the Philips datasheet but couldn't find anything.

    Mode 0 does look much better, but on my TV the 'wide screen' mode chops a bit too much off the left hand side for it to be useable. :(

    NickDvl: Yes, the settings survive reboots - you have to reboot after you've changed the settings to make them take effect.

    What's the lowest bitrate anyone's managed to get working? Down at around 600000 I get a "kb per second too small" message in tverr (and other errors in the kernel log) and the rate appears to default to some higher value.
     
  14. Aug 23, 2003 #14 of 529
    mrtickle

    mrtickle Active Member

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    Note that changing the resolution doesn't alter the recording capacity, only changing the bitrate does. When I changed my high from res 2 to 0 the reported capacity was the same, because the bitrate was the same. The result is that the same amount of movement will produce more artefacts than before unless you increase the bitrate as well.

    According to the other thread I found tivo defaults to Best quality if the bitrate is too small. When it happened to me it basically lied in the tvlog (said it was using the bitrate I had set, but didn't). I didn't think of checking the other logs!
    650000 was too low when I tried. 675000 worked.
     
  15. Sep 9, 2003 #15 of 529
    Dapper Dan

    Dapper Dan Gold Member

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    Have you tried this yet ? I'd be interested to know how you got on.

    As an aside, I was reluctant to up my bitrate in case I caused the mpeg chip to overheat, though for all I know it may be operating well within it's design limits. Can anyone comment ?
     
  16. Sep 9, 2003 #16 of 529
    rharnwel

    rharnwel New Member

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    Surely the higher the bitrate, the less demand on the MPEG chip....?
     
  17. Sep 9, 2003 #17 of 529
    sanderton

    sanderton TiVoer since 11/2000

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    I'd be surprised if you could damage the chip from a software setting.
     
  18. Sep 9, 2003 #18 of 529
    Dapper Dan

    Dapper Dan Gold Member

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    I was thinking of it as a form of overclocking. I'm sure that someone will correct me if I'm wrong, but if you make a chip work harder it runs hotter, this in turn increases the rate of electron migration which eventually causes the chip to fail.
     
  19. Sep 9, 2003 #19 of 529
    iankb

    iankb New Member

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    But, as rharnwel says, the higher the bitrate, the lower the amount of work required to compress it.

    Ian.
     
  20. Sep 9, 2003 #20 of 529
    sanderton

    sanderton TiVoer since 11/2000

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