Friday, December 21, 2012

How "REPEAT" command on LDP-1450 works (detailed)

I didn't want to do any guesswork about how the REPEAT command works on the LDP-1450 so I set up a video capture of a disc running through a REPEAT sequence, complete with VBI lines.

First I search to frame 1 (0x43 0x30 0x30 0x30 0x30 0x31 0x40).

While in STILL frame mode, I issued a REPEAT command using the following bytes:

0x44 0x30 0x30 0x33 0x00 0x00 0x40 (from current position, play til frame 300)
0x30 0x32 0x40 (play through this sequence 2 times)

What this means is:
From frame 1, play until frame 300, then seek back to frame 1, and play again until frame 300 then pause in still mode.

But there are some unanswered questions.  Will it really pause exactly on frame 300?  And when it searches back to frame 1, will we see any of frame 300 before it performs the search?

Hence the reason for me video capture.

Here is what happens:

The full frame 1 is displayed (which makes sense since it was previously STILL'd) as are all the frame up to and including frame 299.  Then the VBI data for the field where frame 300 begins is displayed (I captured it successfully) but the image itself is blanked out and a search begins.  So the actual frame 300 is never shown.

On the second pass (the final pass), it's a little different.

Not only is the full frame 300 displayed, but the disc doesn't pause until it gets to frame 301.  (this struck me as a bit odd but I verified it on a real LDP-1450 so I don't know what to say except it must be right).

UPDATE : This behavior is different depending on which frame we tell it to repeat to.  And the disc I am testing with is a 2:3 pulldown disc which seems to have an effect.  If the frame number occurs in the second field of the frame, the STILL pauses on that frame.  But if the frame number occurs in the first field of the frame, it pauses on the next frame.  At least that's what I've observed.  I guess I will need to test with some other discs.

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