1 Topic by flippu10

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Hello everyone,

I'm a new member.  I recently downloaded the product to try to see if it fits my simple use case.  I'm looking to playback 2 video files, both .avi. 

I'm using the 2 playback screen feature and loaded the 2 avi files.  While playing the videos, first I noticed that the speed of the playback is not realtime so I adjusted to a very low speed to simulate a realtime speed.  Then I noticed that the 2 files are played back at different speed.  I'm using the master control in doing the playback. 

Is there a way to make sure they are played back synchronously?  Also, is there a setting to play it back realtime?

2 Reply by joan

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Hi,
There are several possible cause for mis-synchronization.
What Kinovea version are you using ? (While we are at it, what Windows version ?)

Re: real time playback, do you mean that the speed slider decreases by itself or do you mean that at 100% speed the action is played in too slow/fast motion ?
When in dual playback, both speed slider should be locked (unless specified in the preferences).
Would you happen to be comparing a video taken with a high speed camera with a video taken with a normal camera ? If so, what is the capture framerate of the highspeed video ?

3 Reply by flippu10

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Thanks for the reply.

I'm using Kinovea version 0.8.15 running on Windows 7 SP1.  What I mean by real time is that 100% of the speed of the slider is how fast the actual speed of the video is. So if I have a 30 min video, it will take 30 mins to lay the entire video.  The way the slider is setup, I adjust its speed downward to match the real time speed of the video, typically around 10%-12% speed.

Even with adjusting the speed, it appears that sometimes it speeds up and then slows down.  This happens to both players in a dual mode viewing, independent of each other.

The video file I'm playing is a video of PC screen activities recorded by a software.

When I play the video file using Windows Media or VLC, it plays realtime with none of the issues I mentioned above.

Video properties are: .avi, 4 frames/second, 1017 kbps data and bit rate.

4 Reply by joan

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Please check with version 0.8.23 as the video decoding has been updated.
If the issue is still reproduced, could you send me a short sample for analysis. joan at kinovea dot org.
Thanks

5 Reply by joan

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Thanks for the sample!
I reproduce the problem right away. Unfortunately at the moment I cannot fix it.

It is a unusual file in the sense that it actually has a variable framerate. Basically inside a video file, in addition to the global framerate, each individual frame has a timestamp. Here the video framerate is set to be 4fps, for 5526 frames (23 minutes). What Kinovea does when asked for the next frame is: 1. decode one frame and display it, 2. check the actual frame timestamp, 3. update the frame position in the timeline. This approach works to correct small variations or non integer frame intervals.

It doesn't work with this kind of videos because there aren't really 5526 individual frames. It might be an encoder optimized for screen capture. When the image doesn't change, no frame is saved in the video at all. Whenever the screen does change though, a frame is stored with the proper timestamp. Thus the sequence of timestamps is highly non linear and depends on the content dynamics. But when Kinovea reads the file back, basically being a constant framerate player, it jumps from frame to frame and eats the time gaps in between, giving a much accelerated result.

6 Reply by flippu10

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Thank you for taking the time to analyze it and for the explanation.  That makes sense now as the video appears to visibly jump from frame to frame when there is no activity on the screen.

Is this something you would be able to fix anytime soon? 

I'm in need of a player that would be able to play 2 videos side by side with independent controls as well as a master control.  Your product is perfect for what I need from what I've seen so far.

7 Reply by joan

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No, unfortunately it's not something that can be easily fixed, as the constant framerate assumption is scattered throughout the code.