Video jitter when DTS/DD passthrough enabled over HDMI
#1
Hi,

I am using "Sync playback to display" option and playback is butter smooth on regular 1080p MKVs played with PCM stereo audio. But when I enable DTS/DD passthrough, video play is no longer smooth. It is still quite OK and there are no frame drops but about every second there is minor jitter. It especially visible in scenes with slow / constant moving objects.

I have tried all A/V sync methods [Audio Clock, Video Clock(resample audio) or Video Clock(Drop/Dupe Audio)] and problem remains.

Any hints what is a cause of this?

My system:
XBMC Dharma on Fedora 16
Nvidia GT 520 connected to A/V receiver Marantz NR1402 through HDMI
A/V receiver is connected to SONY LCD (supports 50Hz and 60Hz)
Audio and video over HDMI

Regards,
Rafał
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#2
After some testing I have figured it all out. It turns out that it is not DTS/DD pass-through that causes problems, this option only triggers other settings.

Now what really happens:
If I don't use pass-through, enabling option Sync playback to display makes playback smooth only if option A/V sync method is set to Video Clock(resample audio). Other types of sync methods cause playback to look like with Sync playback to display turned off, that is with jitter.

According to docs Video Clock(resample audio) cannot be used with pass-through, so this the reason why enabling pass-through caused jitter. It just switched A/V sync method to other mode.

The questions are now:

1. Why only Video Clock(resample audio) mode makes playback smooth and others not?

2. My TV only supports 50Hz and 60Hz refresh (no 24p). So although enabling Sync playback to display and Video Clock(resample audio) results in smooth playback it also causes cinema movies to look like TV footage (faster frame rate). Is there any way to have smooth playback on 50Hz/60Hz TV without turning movie into TV news report?

Cheers,
Rafal
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#3
Ok, I have now answer to question 2. My display refresh rate was set to 50Hz which does not match well to 24p movies. So I believe Sync playback to display caused very smooth aliasing of 24 frames to 50 frames, resulting in TV footage feeling.
It seems that when refresh is set to 60Hz which is 2,5 x 24p then Sync playback to display results in 3:3:2 pulldown instead smooth aliasing. In this way I have proper jitter-free playback with cinema feeling.

Still it only works with Video Clock(resample audio), other options of A/V sync method behave the same in 60Hz as in 50Hz. So enabling DTS/DD pass-throuh is still not an option. Not a big problem though as multichannel LPCM over HDMI works fine for me.

Nevertheless I am puzzled what is the answer to question 1). This behavior seems strange to me.

Cheers,
Rafał
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