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Recording Time-Lapse Videos

I just had a question from a user about this via the support desk and since it's well known that I'm not in any way a video expert [grin] I thought I'd post it here as other users might find the answers useful.

Here's the original question:

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Hello, I have a technical question regarding the use of Cam Studio 2.0 for a time lapse video recording application, without using audio recording. I recently created a time lapse AVI file using Cam Studio 2.0 under Windows XP Pro SP-2, using the following Cam Studio settings:

Compressor Microsoft MPEG-4 video codec, version 2
Quality: 100
Set key frames every 200 frames
Capture frames every: 500 mS (1/2 second)
Playback frame rate of output clip: 30 fps

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Microsoft MPEG-4 video codec, version 2 codec properties

Keyframe every 8 seconds
Compression control: 75
Data rate: 3000 kbps

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During this test with Cam Studio 2.0, a 28 minute AVI clip was produced, and a number of popular video editors were used in test this AVI clip as a video input source. However, upon further analysis of video properties of this clip, the following data was noted:

Clip duration: 28:19:06 (28 minutes)
Frame rate: 30 fps
Image size: 1280 x 800 pixels
Pixel aspect ratio: 1.0
Key frames: 168
Delta frames: 39945
Empty frames: 10863

Premiere Pro reports that this Cam Studio generated AVI clip appears to have DROPPED FRAMES.

In having tried this AVI clip with more than one video editor, it was noted that although the clip length was 28:19 minutes (about 28 1/3 minutes) long, in fact when using this source clip for a test rendering, the actual clip length became just slightly over 22 minutes. At first it was baffling why this was so. However, in examining the clip properties above and subtracting the fraction of the empty frames from the total clip length, an EFFECTIVE clip length of about 22 minutes could be arrived at through:

168 key frames + 39945 delta frames + 10863 empty frames = 50976 total frames

(50976 total frames - 10863 empty frames) / 50976 = 78.6899%

28 1/3 minutes x 78.6899% = 22.295 minutes

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Could you please advise how, if possible, these EMPTY FRAMES could be eliminated when using Cam Studio 2.0 to perform time lapse screen capture recording? If this is possible through adjustment of either video options or codec properties, I would be very interested to know of it and re-run the test. As of now, outputted AVI clips from Cam Studio are unuseable in many major video editors as they appear to skip the empty frames and shorten the actual clip length during the rendering / output process. Thank you for your help on the above.


HERE'S MY REPLY:

I am by no means an expert on video, but as I understand it (and feel free to correct me) the "capture frames every" rate when multiplied by the "playback" rate should = 1000.

So for instance in my CS I have:

Capture Frames Every: 50 ms
Playback Rate: 20 fps

My keyframe rate is every 30 frames but I don't think that makes much of a difference.

So if I'm correct (that'd be a first!), and you wanted to record a time-lapse video, you would need to increase the "capture" rate and decrease the playback rate to show the video at normal speed, so something like:

Capture Frames Every: 500 ms
Playback Rate: 2 fps

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Can anyone confirm if I'm correct or should I go stand in the naughty corner?

Cheers

Nick :o)

Comments

  • As you see in the above post, the most important setting change was from

    Capture frames every: 500 mS (1/2 second)
    Playback frame rate of output clip: 30 fps

    To

    Capture frames every: 500 mS (1/2 second)
    Playback frame rate of output clip: 2 fps

    Making the two amounts, when multiplied, equal 1000.

    See this post for a discussion of using much longer pauses between frame captures and how that relates to the expected playback rate (fps)
    http://camstudio.org/forum/comments.php?DiscussionID=430&page=1#Comment_1570

    Terry
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