#27 Timelapse

open
nobody
encoding (5)
1
2004-12-30
2004-03-15
David Liontooth
No

Setting the capture framerate below the default can be
useful for generating timelapse movies.

Currently, if you set the framerate below the NTSC/PAL
default, xvidcap will not produce timelapse movies. For
instance, if you set the framerate to 1 fps, on
playback each frame will last for something like one
second.

There is a similar case where something like the
current behavior would be useful: the case of dropped
frames.

When frames are dropped, and there is a soundtrack, it
would be good default behavior for the last frame to
"fill in the gap" of the missing frame. The resulting
movie would be jerky, but in theory sound would stay
synchronized.

However, in the case of manually set framerates below
the NTSC/PAL default, this kind of "filling in the gap"
behavior is surely not generally useful. Instead, the
default should be that the captured frame stay a single
frame, generating a timelapse movie.

For instance, if you set the frame rate to 1, you
should get a timelapse movie that speeds up time by a
factor of 25 on PAL and 30 on NTSC. Storage
requirements from captured footage would go way down,
so long sequences could more easily be captured.

Cheers,
David

Discussion

  • Logged In: YES
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    Hmmm,

    don't think I want to subscribe to:

    > However, in the case of manually set framerates below
    > the NTSC/PAL default, this kind of "filling in the gap"
    > behavior is surely not generally useful.

    personally I record at 10 fps (MPEG4) most of the time,
    since my test machine is pretty slow and also it will give
    me acceptable quality

    I understand that what you're talking about is the strict
    1:1 relationship between the capture frame rate and the
    playback frame rate. Today the same value is always used
    for both.

    Now, you could have a playback frame rate that's independant
    from the capture rate. Like: capture 10 frames per second
    but play back 20 frames per second.

    the following may be true:
    > Storage
    > requirements from captured footage would go way down,
    > so long sequences could more easily be captured
    but those videos will also play back unnaturally fast?!?

    Is that what you'd like to see?
    If so, I would definetely make that behaviour an option
    only.
    Also, this is going to make a/v sync difficult at best.
    The libavcodec automagically keeps track of when it's time
    for an audio or video frame. I'm pretty sure it looks at frame
    rates to do that.

    And then I'm not sure I understand the use case ...
    to prioritize ...

    Karl.

     
  • Logged In: YES
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    (update: state change to pending and lowering priority)

     
    • priority: 5 --> 1
    • status: open --> pending
     
  • Logged In: YES
    user_id=897748

    Hi Karl,

    "those videos will also play back unnaturally fast?!?
    Is that what you'd like to see?"

    Yes! A timelapse movie plays "unnaturally fast" -- that is
    to say,
    it lets you see in a short time period things that happen
    over a long time period. As you say, this would mean making
    the playback framerate different from the recording
    framerate. If this could be an option, that would be great.
    That way you could monitor something that changes slowly, or
    get a quick impression of something that has been happening
    for a long time.

    It's not a default feature, obviously, but it would be great
    to have this be an option. Capturing a frame a second could
    then be played back at 30 frames a second and you could see
    hours of screen activity in minutes, without taking up a lot
    of system resources while capturing. Good for getting a
    quick sense of some games, for instance.

    Looking forward to the new version! Happy New Year to you!

    Cheers,
    Dave

     
    • status: pending --> open