[vdr] Advice on new motherboard, xineliboutput, vdpau, hdmi video & audio, etc.

Niko Mikkilä nm at phnet.fi
Thu Aug 19 17:00:22 CEST 2010


Hi,

ke, 2010-08-18 kello 10:13 +0200, jori.hamalainen at teliasonera.com
kirjoitti:
> I also would like to remind the framerate issues. Naturally you decide what
> is enough precision and quality for you.
> 
> Computer hardware usually cannot provide 50.000Hz, 59.940Hz or 23.976Hz
> outputs to your TV/Monitor. This will cause some judder on display output
> as MPEG/AVC input-stream is not synchronized to output framerate.

If the difference is only few percents or less, this is not a problem
for playing back recordings. You can simply sync the video playback to
screen refresh and resample audio or drop/duplicate audio samples. That
way there is no video judder and only a very slight reduction in audio
quality.

Heck, even most of the movies broadcast on PAL TV have been converted
from 23.976 fps or 24 fps to 25 fps in a similar fashion; by speeding up
and resampling audio.


> With this bridge we come to VGA-hardware which might have 50.01Hz closest to
> 50Hz signal. So every 100 frames we get a jump in picture synch.

You mean every 100 seconds.


> Ever seen jumping camera panning while watching a film and got annoyed by it?

That's usually due to a much larger framerate mismatch or failure to
configure the video player so that it doesn't drop/duplicate video
frames to keep A/V sync.


> For ATI cards there is a dynamic framerate fix, unfortunately there is not
> one
> for Nvidia cards. Nvidia has good HW acceleration but potentially bad
> output.
> With ATI vice versa.
> 
> This ATI fix fixes 50.01 by dynamically reprogramming VGA timers so real
> output
> is 50.000Hz. (General description, the author can describe more if needed).

The actual problem is that normally neither the video nor the audio
outputs in a PC can be synchronized to _live_ broadcast. When the stream
is live, one can't replay it faster. Slower playback would be possible
with a buffer, but I don't know if anyone has implemented that.

The vga-sync-fields (http://frc.easy-vdr.de/) patch collection provides
support for synchronizing the video output exactly to a live transport
stream. However, it only works on old pre-Avivo Radeons and Intel i9xx.

I'm guessing that most general-purpose network media players such as
Popcorn Hour and PS3 have the same problem with live playback? The only
advantage they may have compared to standard PC hardware is that they
can have a single clock source for both video and audio, which means
that recordings can be played back in sync without dropping or
duplicating audio frames.

--

Niko





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