interlaced video question for you XV experts

[Billy Biggs]

Jon Smirl (jonsmirl at gmail.com):

> A standard TV signal requires interlaced video. How does XV maintain
> sync when playing a video file? For example say I am playing an
> interlaced file to TV out. How is the framebuffer set up, is there one
> full screen progressive buffer that is updated at 30Hz and then
> scanned out interlaced at 60Hz, or is it a half size buffer that is
> updated at 60Hz? If there is an half sized buffer what happens when
> playing interlaced video to a non-interlaced display?

  My understanding (as an application author) is that XVIDEO has no
native support for interlaced video.  When writing to a TV output, you
have no idea.  Rumor had it that the NVIDIA driver was always
top-field-first when you gave it interlaced frames to play on its TV,
and you had to write at 30 Hz to keep up.  Reports of weirdness, loss of
quality, or stutter have been heard.

  There was some talk a while back for having like an XV attribute to
indicate whether the image you just uploaded was a top or bottom field,
but there was never any support added for something like this in the
drivers AFAICT.

  -Billy