Re: Sound lag over HDMI

On 12.07.2013 23:54, Ulrich Sp=F6rlein wrote:
> I'm trying to setup XBMC on a -CURRENT box with an IvyBridge CPU and
> GPU. While testing playback via mplayer on a LG TV over HDMI, I noticed
> that sound is lagging video by about 100-200ms or so. When I switch to
> using the jack outputs powered by some Realtek chip, audio is perfectly
> fine.
>
> Is HDMI lag a known problem? Can this be fixed?
>
> root@coyote:~# dmesg | egrep vgapci\|pcm
> vgapci0: <VGA-compatible display> port 0x3000-0x303f mem 0xe0000000-0xe03=
fffff,0xc0000000-0xdfffffff irq 16 at device 2.0 on pci0
> agp0: <IvyBridge mobile GT2 IG> on vgapci0
> pcm0: <Realtek ALC888 (Rear Analog)> at nid 20 and 24 on hdaa0
> pcm1: <Realtek ALC888 (Rear Digital)> at nid 30 and 31 on hdaa0
> pcm2: <Intel Panther Point (HDMI/DP 8ch)> at nid 6 on hdaa1
> pcm3: <Intel Panther Point (HDMI/DP 8ch)> at nid 7 on hdaa1
> drmn0: <Intel IvyBridge (M)> on vgapci0

I don't know what to say. I am now using HDMI audio from NVIDIA card to =

quite old external 5.1 receiver with XBMC every day, and I haven't =

noticed lags. Before that I've also successfully used SPDIF connection =

for the long time. Though I've never specially tested it somehow other =

then watching movies. :) If you have some good testing methodology -- =

please, welcome to share. By the HDA driver HDMI is handled exactly the =

same way as analog output from the point of data buffering, so I would =

not expect there major differences.

You may try to experiment with hw.snd.latency sysctl to tune buffering =

in kernel to see whether it affect the result.

Also you may compare delays when doing AC3/DTS pass-through with case of =

software decoding and discrete (multichannel) PCM playback.

The only potentially related effect I have noticed is that my receiver =

eats first second or about that of playback stream. It makes short =

sounds like GUI event notifications inaudible sometimes. I guess that =

could be made to restore audio sync after some unavoidable startup =

delay, but that is only my guess.

-- =

Alexander Motin
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