Re: Vertical synchronization

[surya <surya@xxxxxxxxxxxxxxxxxxxxx>]

Hi Michael and all,
  I have been asking the question whether BT8x8 cards write video data
directly on to the framebuffer many times. But I got the answer from
your mail. If BT8x8 cards write video data directly on to the
framebuffer, how can we read the video data from "/dev/fb0" instead of
"/dev/video0" ? I am using Microwindows (www.microwindows.org) to
develop a tv viewer application like "Xawtv" which uses "/dev/video0" to
read video streams. I have planned to develop a tv viewer application
which reads the data from "/dev/fb0".

On Mon, 2003-12-29 at 22:07, Michael Hunold wrote:
> Hello Leonid,.
> 
> > is there way to "catch" vertical frame (field) synchronization 
> > using BT8x8 cards and bttv driver ?
> 
> You have to distinguish between the synchronisation of your image source
> (ie. the bt8x8 card) and the synchronisation of your output (ie. your 
> graphics adapter).
> 
> In overlay mode (ie. when the bt8x8 is writing directly to your 
> framebuffer) there is nearly no way that you can synchronize these two, 
> especially if you're using a TFT. While the video is incoming with 25 
> frames (or 50 fields) per seconds, the TFT is usally displaying it's 
> picture with 60 frames per seconds.
> 
> In grabbing mode (ie. when the bt8x8 writes the picture to some 
> offscreen memory), the synchronisation of your incoming picture is not 
> important.
> 
> What you really need is a way to synchronise the output, ie. a way to 
> tell your output device: "wait for the next vertical sync, then flip to 
> the next frame, so I don't get any tearing effects".
> 
> I don't know if X finally has something (ie. a "X vsync extension") like 
> this, otherwise you need to use some other toolkit like DirectFB 
> (http:/www.directfb.org) that lets you sync your output to the vsync.
> 
> > Regards,
> > Leo.
> 
> CU
> Michael.
> 
> 
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-- 
S.Suriya Mohan, MCA.
Software Engineer,
Insys Technologies,
Coimbatore-641001.
India.

There is no substitution for hard work.