[mythtv-users] Bob deinterlacing drops frames, but not high CPU

[Matt Doran]

Doug Larrick wrote:
> Matt Doran wrote:
>   
>> It's 25fps DVB broadcast (I'm in australia).  I've got my X vertical 
>> refresh is 50Hz, because I was under the impression this should lead to 
>> smoother scrolling (i.e. an integer multiple of the frame rate).
>>
>> Is that what you were after?
>>     
>
> Yup.  You've got that set up right.
>
>   
>> Another thing that may or may not be useful.  I'm not using the OpenGL 
>> sync method, because when I enable it, I get a very subtle mismatch 
>> between audio and video ... and no frame drop messages.  So I'm using 
>> the RTC video timing.  
>>     
>
> I think this is your problem.  RTC calculates when the next frame should
> show up, but has no feedback from the video display.  So occasionally
> the video card waits an extra frame (or plays too early)... when enough
> of these add up, we skip a tooth and you get your message.
>   
Thanks Doug.  You really seem to know about this stuff....

OK.  So what methods will work?   Only OpenGL?

I've looked through the code, and the sync options are tried in the 
following order (the first valid option is selected): nVidiaVideoSync, 
DRM, OpenGL (if enabled), RTC, then the BusyWaitVideoSync (which I was 
using earlier, but also doesn't work well).

I assume the nVidia one would be the best??  But I get this in the logs:

    nVidiaVideoSync: VBlank ioctl did not work, unimplemented in this
    driver?

Should this work for my card?  Or is OpenGL sync the best option?

> Also look for the message "Refresh rate: xxx, frame interval: yyy"
> (which is under --verbose general or playback, not sure which) to see if
> Myth's estimation of your refresh rate is what you're expecting (note
> that this is interval in usec, not frequency in Hz).
>   
This is what I get.  Is this good/bad??

    Refresh rate: 20040, frame interval: 40000

> You know there's an adjustment for audio/video sync, right?  During
> playback hit "menu" and it's listed in the OSD menu.  There may be a
> direct keybinding too; not sure.
>   
Yes I do.   But if this delay happens for all video, is there a global 
setting so I don't need to change this each time I start.
> It's also possible your soundcard is the culprit if its timing is off.
> Try enabling extra buffering if it's not already; if you have a spare
> soundcard lying around you might try that as well.  Or try "use video as
> timebase" (unless you're using AC3 or DTS passthru, which is incompatible).
>   
I am using AC3/DTS passthrough.  And the problem only appears when 
OpenGL sync is enabled.  It's very subtle problem, .... I'm not even 
100% sure it's not dropping frames.... it's hard to put my finger on but 
it looks odd.   I guess I'd be seeing messages in the log if it was 
dropping frames, wouldn't I?

Thanks for your help,
Matt