gregjohn <pte### [at] yahoocom> wrote:
> Q: Is this DRM, in the sense that someone made them set up movie players that
> way, or is it an inevitable and unintended function of the way computers handle
> moving vs. still images?

  It's frame buffer optimization. Nothing to do with DRM. This feature has
existed for long before DRM was even an idea.

  The player (usually using DirectX, or in Linux by using the video driver)
is not drawing the video on your screen memory at all, but to a frame buffer.
A frame buffer is a separate chunk of RAM which has been mapped to the
video card by the memory bus.

  In the actual screen memory the pixels in the area where the video should
appear have a certain color. When the video card detects pixels of that
color inside that area, it will substitute them with the contents of the
frame buffer instead. (This allows even the screen to have a different
bit depth than the frame buffer, which allows eg. having your screen to
be in paletted 8-bit mode, while the video player is showing the video
in full color mode.)

  When you make a screen capture, you are simply capturing the screen memory,
and thus you are only get those specially-colored pixels. The screen capture
routine knows nothing of frame buffers.

  You can turn this frame buffer optimization off, after which the screen
capturing becomes possible. In Windows there is a setting somewhere which
you can use to set the level of video acceleration. Lower it until you can
screen-capture your video. (Obviously screen refreshes may become quite
sluggish.)

  If you are using mplayer in linux, simply play the video with -vo x11
and you'll be able to screen-capture it. (The x11 driver does not use
hardware acceleration.)

-- 
                                                          - Warp

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