[mythtv] [mythtv-commits] Ticket #1219: LiveTV takes a while tostart, and video jerks forwards

Mark Spieth mark at dclabs.com.au
Tue Feb 7 00:08:05 UTC 2006

> On Tue, 2006-02-07 at 08:11 +1100, Mark Spieth wrote:
>> daniel,
>> basically, dont start/unpause audio until the first frame is displayed.
>> the only problem now is that it doesnt start at the beginning but that is
>> another problem. works well with slow machines too. may or may not fit in
>> with your ideas on what is wrong.
> I don't have much of a theory on what is going wrong since I can't
> reproduce the problem. Why don't you finish the patch and have the
> reporter try it out. If it helps then reopen the ticket with the
> patch and assign it to me. Then I'll check it out.
> It seems plausible at least that his machine is having trouble
> resyncing to the audio if it takes a while for the video to
> initialize... The logs he posted did show a pretty long audio
> sync, though I discounted that since the log is from before
> some of Isaac's most recent fixes for ringbuffer switching.
> It's weird though since even my slow old P4 1.8GHz machine
> doesn't have this problem with even 1080i material.
may be a memory thing. if you dont have enough a bit of swapping has to 
occur. I have an XP2000+ (BE+FE) with only 256M and starting a recording has 
3 phases:
audio for 1 sec, no video
no audio for 1 sec, no video
then plays correctly.
this fixes that problem. you are correct it takes a while for video to 
initialize, sometimes 5-7 seconds. pretty sure its related to swapping.
havent tested live tv yet with this patch, only recordings.
it also appears that opening a file advances the first frame played to the 
2nd I-frame. this is quite noticable in avi's which have long inter-I 
also I have noticed that with alsa out, pausing introduces a jerk due to the 
500ms buffer set up in it. Ive set this to 100ms for me and is much nicer. 
never had this problem with oss due to its fixed size buffer. not sure why 
this was set to 500ms in the first place. seems to long to me.

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