[mythtv-users] frontend error messages prebuffer wait timed out

[Michael T. Dean]

On 02/01/2009 09:47 AM, Jean-Yves Avenard wrote:
> 2009/2/2 Michael T. Dean:
>   
>>> Does anyone have any ideas?
>>>       
>> http://www.mythtv.org/wiki/Prebuffering_pause
>>     
>
> I've had exactly this issue on my machine. Once in a while, the
> picture would freeze and I must exit LiveTV and comes back. Would
> happen every few hours or so...
>
> That wiki didn't provide me any answer.. I tried everything they
> mention and it made no difference.
> My machine is fast enough (3.16GHz C2D, sufficient RAM and fast
> network: gigabit). And so is the backend... 4 drives in RAID5 with
> over 1TB of free space and 2.8GHz C2D with plenty of free RAM.
>
> After a few experiment, this is what fixed it for me:
>
> In general config, I've unchecked "Aggressive Sound card buffering"
> and in TV Settings -> Playback, I have checked "Extra Audio Buffering"
>
> Now the picture does freeze every few hours or so, but only for a
> second or two, and I do not have to exit LiveTV anymore..
>
> What an improvement!

Yeah, the setting:

Aggressive Sound card Buffering
If enabled, MythTV will pretend to have a smaller sound card buffer than 
is really present.  This may speed up seeking, but can also cause 
playback problems.

exists /solely/ for the benefit of people using underpowered frontends 
that can't decode audio quickly enough to keep up with the buffer that 
Myth normally uses, so Myth uses a smaller buffer so it doesn't have to 
stay so far ahead of the video.  Note that decoding audio is easy 
compared to decoding video, so if you have a borderline HDTV setup, this 
setting will not help at all (i.e. the processor savings from using this 
setting are negligible compared to the processor resources required for 
decoding HDTV video).  Therefore, it's only useful for people using 
underpowered SDTV-only systems.  This setting should almost /never/ be 
enabled (it was really designed for use with the early Via systems that 
were running a < 1GHz).

The setting:

Extra audio buffering
Enable this setting if MythTV is playing "crackly" audio and you are 
using hardware encoding. This setting will have no effect on MPEG-4 or 
RTJPEG video. MythTV will keep extra audio data in its internal buffers 
to workaround this bug.

is meant to allow Myth to "ride out" low-bitrate areas of the MPEG-2 
video by keeping a larger audio buffer.  This setting is useful for any 
MPEG-2 video (including that produced by hardware encoders such as the 
PVR-x50's, as well as DVB or ATSC MPEG-2).  For this reason, the trunk 
version of the help text reads:

Extra audio buffering
Enable this setting if MythTV is playing "crackly" audio.  This setting 
affects digital tuners (QAM/DVB/ATSC) and hardware encoders.  It will 
have no effect on framegrabbers (MPEG-4/RTJPEG).  MythTV will keep extra 
audio data in its internal buffers to workaround this bug.

The setting will never do any harm if enabled (even if not using 
MPEG-2)--except on the same class of systems that the "Aggressive Sound 
card Buffering" setting is meant to help (and, then, only if those 
systems are decoding MPEG-2 SDTV).  Therefore, this setting should 
/always/ be enabled (again, except for the systems that the "Aggressive 
Sound card Buffering" setting is meant to help).

Note that the two settings are virtually opposites (so they should never 
be enabled together).

So, Jean-Yves's advice is good--disable "Aggressive Sound card 
Buffering" and enable "Extra audio buffering".

I guess I should add that to the Prebuffering Pause wiki page, as well 
as the other invalid mythfrontend config that can cause Prebuffering 
Pauses, the "Use video as timebase" setting (which should be disabled, 
as its help text implies).

Mike