RFC: Xv field order

[Thomas Hilber]

On Wed, Jun 24, 2009 at 07:33:47PM +0200, Krzysztof Halasa wrote:
> I already wrote about the difference and not about a card only, right?
> The broadcast is the most accurate and stable (at least here), almost
> always at 50 Hz +- maybe 10 ppm, maybe less than that.

finally it does not matter how stable the broadcast itself is. 
Rather how this stability is realized by the decoder.

> Of course. That's why I wrote about a buffering.

Buffering if at all only would help if your graphics card is slower
than the broadcast. If it's faster you get noticeable disturbances if
your buffer gets exhausted.

> No. In fact, I have just verified with a freq meter, it's orders of
> magnitude better. Aren't you using a miscalculated modeline (not 13.5

even that is way too much if you want directly route interlaced fields
from decoder to graphics card double buffer. Without dynamically syncing
decoder and graphics card you have no chance to stay within a time
window of about +-20ms for double buffer updates.

> MHz pixel clock or invalid total number of pixels or lines or something
> like that)? 0.2% difference is excessive.

I'm not speaking of my own setup. My algorithm dynamically adjusts with 
accuracy of +-0.001Hz. I'm speaking of common solutions for video 
playback using the XV extension.

> That would be true if you use some player-internal time base. But
> players can, and do, synchronize to the graphics card. IOW the card
> becomes the time base, and everything (sound) is adjusted to it.

are these solutions also available for live TV?

> Depends on the output driver. I think all "sync" drivers for mplayer
> and xine do it, don't they? (E.g. matrox driver)

can't tell. I don't know these proprietary solutions for matrox cards.

> Now the question is the interface between players and Xserver, not the
> internals of the driver, which BTW I'm using for almost two years
> without issues.

no problem. With my solution I setup a tiny D945GSEJT based linux SAT
receiver consuming only about 14W with high quality SCART/HDMI output.

I don't know any another solution providing these features under linux.

- Thomas