[mythtv] Buffer Time stamps

Andrew Kimpton awk at awkward.org
Sat Aug 12 12:34:45 UTC 2006

I'm working out some kinks in adding Plextor Convert-X support to the  
backend on Mac OS X. I can transfer video and and audio fine from the  
device (and initialize it, do channel changes etc). But...

I'm getting exceedingly 'glitchy' (stuttering) audio playback and a  
lot of :

NVP: Prebuffer wait timed out 10 times

messages from the frontend.

I know that my machine is not overloaded (I can use Shark on Mac OS X  
to see that between them the frontend and backend only use 65% of the  
CPU on my machine). So I think something must be going wrong with the  
time stamps being placed on the buffers in NVR::BufferIt and from the  
NVR::doAudioThread. Can someone give me a brief synopsis on how this  
is supposed to work, and also what the player side does with the time  

What I'm doing closely follows the existing GO7007/V4L2 code -  
BufferIt applies TimeStamps based on 'now' (I've not changed BufferIt  
at all) and my doAudioThread (which is new) timestamps the received  
USB buffers using the same mechanism as the existing GO7007/V4L2 code.

Also there's probably a better way on Mac OS X to get timing  
information than calling gettimeofday - however I'd like to  
understand the expected resolution and units of the timing info. It  
looks like the buffers are stamped with a delta in milliseconds since  
the NVR thread started - is it that simple ?


Andrew 8-)

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