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

Niko Mikkilä nm at phnet.fi
Fri Aug 20 15:38:21 CEST 2010


Fri, 2010-08-20 at 10:08 +0200, jori.hamalainen at teliasonera.com wrote:
> > There is no graphics card, BD/DVD player or other standalone device that
> outputs 
> > those rates exactly. I don't know how much they deviate, but I'd guess
> it's usually 
> > something like 0.01 % (50.005 Hz instead of 50 Hz), as Jori said.
> 
> If you can find a modeline what your output is currently using you can use
> online services
> to check framerates it provides.

"xvidtune -show" prints the current modeline, but the refresh rate
calculated from it will not be the same as the actual rate. The clock
chrystals have deviations in order of 0.01 % and the only way to fix
that is by adjusting the timing slightly at frequent intervals as
vga-sync-fields does.

Having a more accurate time source might not help either because the
broadcast may not be accurately timed.


> It does not help using direct Toslink-output from VDR which mostly prohibits
> resampling of audio.

Audio can be resampled with any PCM output. The idea is to adjust the
playback speed slightly by resampling for example 48 kHz audio to 48.01
kHz and then playing the result back at 48 kHz.

This is more difficult if you'd like to play multi-channel AC-3 with
S/PDIF passthrough; then the audio would need to be decoded, resampled
and re-encoded. An easier alternative is to drop/duplicate AC-3 packets,
but that may be more noticeable on playback.

Both Xine and XBMC support resampling audio. XBMC also supports
dropping/duplicating audio packets.


> And why would you like to have audio decompressed, speeded up 1%
> and then 
> recompressed.
>
> Just to avoid your output software to duplicate or drop frames. Synch
> perfectly..

Yep, that's the best way to get fluid video playback with synchronized
audio on current PC hardware.

Re-encoding is unnecessary with stereo streams or HDMI1.3 and analog
multichannel outputs. High-quality resampling is totally unnoticeable.

--

Niko




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