Why does digicam's max video rec time differ?

Discussion in 'Digital Photography' started by DaveC, Aug 10, 2012.

  1. DaveC

    DaveC Guest

    When I take a video with my Canon PS G9 it will automatically stop recording
    anywhere from 20 minutes to 1 hour. Why such a variance?

    Battery is not the issue: I can start another video and likewise it will
    record for a similar time.

    The manual says that 4 GB is the max video file size it will record (indeed,
    the files are all 4 GB), but that the max time will vary. The manual says:

    "Even if the clip size has not reached 4 GB, recording will stop at the
    moment the clip length reaches 1 hour. Depending on memory card capacity and
    data write speed, recording may stop before the file size reaches 4 GB or the
    recording time reaches 1 hour."

    My question is: what variables cause the max time to vary? If I'm using the
    same memory card (SDHC, Samsung 32 GB, class 10), why not identical video
    times?

    (These tests are done with identical settings: when a video has stopped
    recording I just push the shutter button again.)

    Thanks.
     
    DaveC, Aug 10, 2012
    #1
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  2. DaveC

    MC Guest

    Same reason no two photos taken of the same scene/subject are ever spot
    on with reagards file size. It's all to do with image/frame/scene
    complexity and how the software renders each of these frames. You will
    very rarely encounter two identical frames on a video. This could even
    come down to the slightest change of light or slight movement, changes
    that may not even be distinguishable by the human eye. Each 4GB video
    will vary in time because the more complex the scene or rendering
    requirements the shorter the video will be, in time.
    For example, if you set your camera filming a static scene of a plate
    of cakes you will get a far longer 4gb video than if you set your
    camera filming the goings on at a lively childrens party, where the
    scene could be changing quite drastically each and every frame.
    Something like that, anyway.

    MC
     
    MC, Aug 10, 2012
    #2
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  3. DaveC

    Martin Brown Guest

    It depends strongly on the compressibility of the material in the MPEG
    stream (or whatever method that camera used). An active scene with
    people moving panning and/or zoom will require a lot more storage space
    that a picture of a still life arrangement of fruit on a table.
    The 4GB is a hardware limitation of the file system typically used on
    removable media. Even proper video cameras often split long files every
    4GB to deal with this limitation. The 1 hour timeout is artificial and
    imposed by the manufacturer fairly gratuitously.

    I have to say that my Inxus 100IS burns through its battery when taking
    video and becomes quite hot after about 5 minutes.
    If you film a static scene with MPEG encoding it will be rather easily
    compressible.

    Regards,
    Martin Brown
     
    Martin Brown, Aug 11, 2012
    #3
  4. DaveC

    David Taylor Guest

    On 11/08/2012 09:43, Martin Brown wrote:
    []
    IIRC, there is a 30-minute cut-off so that in Europe the camera cannot
    be regarded as a "video" camera, and therefore escapes some particular
    tax, but I might be wrong.
     
    David Taylor, Aug 11, 2012
    #4
  5. DaveC

    Bruce Guest


    That was true a couple of years ago, and certainly in the era of the
    Canon PowerShot G9, but I believe the rules have recently been
    changed. My UK-purchased G9 would only record video up to 29:59.

    Of all the cameras I have bought and sold over the years, the G9 is
    probably the one I most regret selling. :-(
     
    Bruce, Aug 11, 2012
    #5
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