[mythtv-users] Strange Playback behaviour
Peter Bennett
pb.mythtv at gmail.com
Tue Oct 9 14:32:15 UTC 2018
On 10/09/2018 10:03 AM, Allen Edwards wrote:
>
>
> On Tue, Oct 9, 2018 at 6:31 AM Stephen Worthington
> <stephen_agent at jsw.gen.nz <mailto:stephen_agent at jsw.gen.nz>> wrote:
>
> On Tue, 9 Oct 2018 13:39:14 +0100, you wrote:
>
> >On Mon, 8 Oct 2018 at 15:27, Peter Bennett <pb.mythtv at gmail.com
> <mailto:pb.mythtv at gmail.com>> wrote:
> >>
> >> The speed up and slow down problem is likely related to the
> audio. It
> >> tries to vary the video rate to keep in sync with audio. If it is
> >> getting bad audio timestamps or bad information from the audio
> driver
> >> this can happen. Run with -v playback and look at the log for
> >> confirmation. If this is the case I suggest trying different audio
> >> settings. Also there is a setting you can try. Run mythfrontend
> with -O
> >> AVSyncAveraging=60. The minimum and default value is 4. You can try
> >> different values. Higher values will smooth out the speed
> changes but
> >> may cause lip sync problems.
> >
> >Thanks for the tip, I turned on the playback logging and here is a
> >link to part of the log during a couple of minutes of watching a
> >pre-recorded program. http://paste.ubuntu.com/p/4c6nPpYTwC/
> >
> >Not sure what all these messages indicate, some, like this one :-
> >
> >Oct 8 21:34:03 mustard mythfrontend.real: mythfrontend[18401]: W
> >CoreContext audio/audiooutputalsa.cpp:243 (IncPreallocBufferSize)
> >ALSA: Try to manually increase audio buffer with: echo 128 | sudo tee
> >/proc/asound/card1/pcm7p/sub0/prealloc
> >
> >are obvious and I have attended to this now but not yet tested.
> >Others such as this one could be fixed (the device is owned by root
> >and mode 600) so that is where I was going to go next (1 step at a
> >time right ?)
> >
> >Oct 8 21:34:05 mustard mythfrontend.real: mythfrontend[18401]: E
> >CoreContext vsync.cpp:358 (TryInit) VSYNC: RTCVideoSync: Could not
> >open /dev/rtc: #012#011#011#011eno: Permission denied (13)
>
> This is what I did to fix the /dev/rtc problem. The /dev/rtc device
> is a link to /dev/rtc0, so I created a file
> /etc/udev/rules.d/10-local-rules and put this in it:
>
> # Allow MythTV (mythtv group) access to the rtc hardware for
> mythfrontend to use it for timing.
> KERNEL=="rtc0", GROUP="mythtv", MODE="0660"
>
> So now my rtc devices look like this:
>
> root at mypvr:/etc/udev/rules.d# ll /dev/rt*
> lrwxrwxrwx 1 root root 4 Oct 8 04:30 /dev/rtc -> rtc0
> crw-rw---- 1 root mythtv 249, 0 Oct 8 04:30 /dev/rtc0
>
> and mythfrontend is happy:
>
> mythplayer.cpp:1832 (InitAVSync) Player(11): Video timing method: RTC
> _______________________________________________
>
>
> Can you enlighten me as to how widespread this problem is?
> Specifically, would my new Mythbuntu 14 have this problem? Watching
> DWTS last night the playback was terrible. Much worse than the same
> hardware with Mythbuntu 8, my pre upgrade version. I thought it might
> be fixed with the new 750 video card which I plan to give another try
> at installing today but this post makes me wonder. Some of the dance
> moves were impossible, nobody can move that fast without "special
> powers". Do I need to do something to my system to fix timing?
>
> Allen
>
Run with -v playback and check for messages that say something like
"video is xx frames behind audio, dropping frame to catch up". You can
also try the setting mentioned above (-O AVSyncAveraging=60). I have
written a new synchronization routine to help with some of these issues,
but I don't know if it will help in your case. Let me know if you get
the dropping frame messages or if the AVSyncAveraging works.
Peter
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