[mythtv] Slight choppiness question

skrpub skrpub at earthlink.net
Thu Aug 7 22:22:12 EDT 2003

I have noticed this too on my Athlon 1800 with 480x480 video. CPU is 
usually around 40%, so I don't think cpu is the problem. It gets much 
worse at 640x640 when cpu is 60-70%. I also notice it gets worse on 
complicated scenes. So it is related to data volume, but I'm sure its 
not disk either. I started looking into it in 9.1, but its still there 
in 10.

I haven't tracked anything solid yet, but I'll tell you what I know. My 
myth box is connected only to TV and no keyboard, so I started looking 
at a myth frontend on a different box.

There I found was that it would often wait 1/10 to 1/2 second waiting in 
RingBuffer::ReadFromBuf for data from the socket to fill the buffer, 
even if it was minutes behind the live recording. (For some tests, I set 
the resolution high and tuned to a channel with less than optimal 
reception, so there was some static in the picture. That gave very 
choppy video with the 1/2 second pauses.) There is a loop there that 
waits until ReadBufAvail() returns a large enough count. It often goes 
through the loop a dozen times, with each sleep actually being around 
20ms instead of the 100us specified due to scheduler and timer resolution.

It appears as if the readahead thread isn't reading when it can and 
waits until the buffer is too low. At that point, it takes too long to 
read while the consumer is waiting. That's as far as I got when I got 
sidetracked. Maybe its a good enough pointer that someone else will pick 
it up and run with it.


Sam N. Max (snx) wrote:

>----- Original Message ----- 
>From: "John Hurliman" <jhurliman at focustheater.com>
>To: "Development of mythtv" <mythtv-dev at mythtv.org>
>Sent: Thursday, August 07, 2003 12:50 AM
>Subject: Re: [mythtv] Slight choppiness question
>>Have you tried turning off deinterlacing in myth to see if the
>>choppiness goes away? You might be just a tad short on cpu power.
>Deinterlacing was already off which is probably why I can see some of the
>interlacing issues, though having it on or off doesn't really change the
>choppiness.  Before I was using it on a monitor with deinterlacing on.
>I think with my current settings the tv tuner nor MythTV are doing any extra
>post-processing.  With the flicker filter off through nvtv and my resolution
>settings at 640x480, I don't think the card is attempting any rescaling or
>cleanup to attempt to make things like text more readable.  My hope is that
>with these settings every other line written to the screen by MythTV
>corresponds exactly to a line on a field of the video, so that the tv can
>smoothly display the interlaced video stream as it was originally recorded.
>Note that the choppyness isn't *that* noticable except with things like
>tickers.  It's fairly acceptable otherwise, though I can see it's a tad off.
>Has you or anyone else been having more success with the smoothness of the
>video to the point where thing like news tickers look perfectly smooth?
>- Eron
>mythtv-dev mailing list
>mythtv-dev at mythtv.org

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