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trying to use tracker with a 70 minute video
Rita Elaine Silver
2 Posts

am trying to use tracker to track a teacher's motion through a classroom throughout a lesson of about 70 minutes. Two issues come up: when I load the video I get an errors 'the first frame is not a keyframe'. Have looked through the various threads and checked those referring to opening files, importing files, etc. Based on all that, I tried encoding in different formats, using Xuggle or Quicktime -- error persists. BUT the video does open so maybe that is not a problem?
What concerns me most - when video is open, I get only a snippet, about 20 seconds of the lesson. Where is the rest of the video? Can Tracker be used for such a long video? Are these two issues related?


Replies to trying to use tracker with a 70 minute video

Re: trying to use tracker with a 70 minute video -
John Macuk
3 Posts

I don't think tracker is designed to handle such large videos. You might also check that it's in an accepted format.

John Macuk



Re: trying to use tracker with a 70 minute video -
Douglas Brown Avatar
Douglas Brown
339 Posts

If the video is loading and playing then you can probably ignore the Xuggle keyframe warning (it could be related to the 20-seoncd limit but not likely).  But it is true that a 70-minute video is going to give Tracker problems since it has to convert every frame to a Java image for analysis. I suggest you cut the video into sections of 10 minutes or so and see how that goes. You can always combine the data in Excel.

If you still have problems, then try converting to a different format using a free video converter like Freemake. Xuggle always works well with the FLV format.  Doug

> Re: trying to use tracker with a 70 minute video > > am trying to use tracker to track a teacher's motion > through a classroom throughout a lesson of about 70 > minutes. Two issues come up: when I load the video > I get an errors 'the first frame is not a keyframe'. > Have looked through the various threads and checked > those referring to opening files, importing files, > etc. Based on all that, I tried encoding in different > formats, using Xuggle or Quicktime -- error persists. > BUT the video does open so maybe that is not a problem > > What concerns me most - when video is open, I get > only a snippet, about 20 seconds of the lesson. Where > is the rest of the video? Can Tracker be used for > such a long video? Are these two issues related?



Re: Re: trying to use tracker with a 70 minute video -
Rita Elaine Silver
2 Posts

Thanks will try that.



Re: trying to use tracker with a 70 minute video -
Jim Deane Avatar
Jim Deane
1 Posts

I would consider using something like FFMPEG to cut the video down to perhaps one frame every five seconds.

I don't know what kind of granularity you need in the teacher movement, but I doubt that you really need 30 frames per second. Since tracker can handle different framerates, cutting to one frame per five seconds would cut your 70 minutes of video down from 126,000 frames to 840 frames. Even one frame per second would cut it down to 4200 frames.

Should be a dramatic reduction in memory and processing overhead.

Now, one thing I ran into looking into the feasibility of doing this, is that H264 encoded video (e.g. MPG video) might seriously lose image quality doing this. You might convert to .avi (using ffmpeg as well) and then drop the avi framerate.

If I acquire free time in the foreseeable future I'll use a sample video and try it out myself...


Jim Deane


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