[Bug 64503] audio glitches when running at 24hz/24p

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=64503

--- Comment #14 from Andy Furniss <adf.lists at gmail.com> ---
(In reply to comment #0)
> (originally reported to Fedora:
> https://bugzilla.redhat.com/show_bug.cgi?id=954009)
> 
> I've recently started trying out 24 Hz again as my TV handles it better, and
> XBMC is finally at a point where they can keep things synced up when playing
> at exactly the monitor refresh rate.
> 
> Unfortunately that broke the HDMI audio output. If I try to output audio
> when the refresh rate is at 24 Hz, the receiver will lose audio sync every
> few minutes, resulting in silence until it regains sync.
> 
> I've tried the following:
> 
>  - Sending audio over SPDIF from the onboard audio to the same receiver
> works fine. Another cable though, and cannot handle high-bitrate formats, so
> hardly a long term solution.
> 
>  - Audio format doesn't seem to matter. I get glitches with PCM, AC3 and
> DTS. DTS is the worst, but that might just be because it requires more
> effort to sync back up again.
> 
>  - It's not xbmc that gets confused as sending audio from an entirely
> different program results in the same audio glitches (I tried mplayer with
> -vo null in the background).
> 
>  - Doesn't seem to be a application buffering issue as I see no spikes in
> either xbmc's or mplayer's sync statistics when the glitch appears.
> 
> 
> This is with kernel-3.8.7-201.fc18.x86_64.

Well I guess my bare bones LFS setup is very different to fedora, but I can't
reproduce this.

Kernel drm-next recent-ish with radeon HD4890. Can only test PCM into TV with
mplayer + alsa (pulse not installed)

cpufreq set to performance, GPU on low. TV screen set below monitor screen.

Tried 11 minute 44.1k CD track and 20 mins of blu-ray -vo vdpau 48k stereo and
didn't hear any glitches at all. Of course blu-ray was 23.976 and modeline was
24, but I doubt that's relevant, mplayer will tweak video rate to keep audio
sync and -framedrop was given.

FWIW this is my 24Hz line as shown by xrandr --verbose, maybe yours is
different?

1920x1080 (0x2cd)   74.2MHz +HSync +VSync
        h: width  1920 start 2558 end 2602 total 2750 skew    0 clock   27.0KHz
        v: height 1080 start 1084 end 1089 total 1125           clock   24.0Hz

Having never used pulse I don't know if it's easy to bypass (assuming you are
using it),

mplayer -ao alsa:device=hw=1.3 may work (assumes cat /proc/asound/cards shows
HDMI as 1)

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