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Elancheran

Trying to play the video in Reverse

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Hi Everyone,

      I am trying to play the video in reverse decrementing the frame number in IMAQ Read Frame function. Its working but the result is very choppy as every frame takes significant time to load, but when I just increment the frame number and play the video forward, its executing without any problem. I have attached the VI and info regarding the video, could you guys please let me know why I am having problem when I am trying to display the video in the reverse order.

Playing AVI file.vi

Video Properties.png

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Shootballing. It may very well be that the codec used for that video is incremental, so that only certain differences from the preceding image are encoded in the next. That at least is one of the tenets of mpeg. If that is the case, I wouldn't be surprised that reconstructing what looks as an innocent predecessor requires in fact to read much more information from disk, and perhaps more computation, than a successor. If so, that seem a characteristics of the codec used rather than a limitation of LV. For reversibility, perhaps a different codec should be considered.

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mjpeg doesnt work like that, its literally a bunch of jpegs in a wrapper. Random access should work as well as forward access. I'd bet forward access has some caching and pre-fetching though, so for random access check your cpu load, memory, and disk usage while trying to play the video. I'd bet you're hitting some limit. Specifically you are asking a lot of windows to smoothly unpack a randomly accessed frame every 34 ms using software decoding. 

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