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magic timewarp number?

Last post 11-29-2009, 10:17 by simonbaker. 2 replies.
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  •  11-26-2009, 14:26 357337

    magic timewarp number?

    Theoretically, if I capture a clip at 50i and put it on a 59.94 timeline, then apply a "magic" timewarp amount, each frame from the 50i clip should slot perfectly into a frame on the 59.94 timeline, no interpolation or processing needed (assuming all else is the same between formats, such as color depth, etc.).

    In other words, conversion should be blazingly fast.

    The magic number should be a timewarp of 59.94/50 (clip speed), I would think.

    However, I have not been able to achieve this "blazingly fast" conversion with any magic number.

    Does anyone know if this is possible with the LE timewarp algorithms?  I'm sure somewhere is a Pinnacle engineer who could answer this question.  Or maybe Smetvid?

  •  11-26-2009, 15:51 357351 in reply to 357337

    Re: magic timewarp number?

    ....aahhh, you're forgetting that regardless of whether you shoot 50i or 59.94i (assuming we're talking DV or HDV) the data rate doesn't change - it stays constant at 25Mb/s. The amount of data used in each field/frame is NOT the same when using 50i or 59.94i. Therefore - logically - if you play back material that is shot at 50i at a frame rate of 59.94, you are increasing the data rate by a factor of (approx) 1.2. Therefore you are no longer within the specifications of DV or HDV. Also, when you've created a timeline, you've specified the render codec for that particular timeline. That codec also specifies the data rate to be used so, when you place your 50i footage on a 59.94i timeline, you're "speeding up" the footage, but you also need to reduce the data rate by a factor of 0.83 in order to now reduce 59.94i frames of 50i data into a 59.94i data stream... It's one thing to come up with a magic number to create a 1:1 frame correlation - it's something else entirely to fit it withing the constraints of the various codecs....

     .....and if your talking DV as opposed to HDV, you need to realise that there are a lot of calculations going on as everything is resized from 720x576 to 720x480....

     Personally, I think that forty-two sounds like a blazing-fast number....   Stick out tongue

  •  11-29-2009, 10:17 357849 in reply to 357351

    Re: magic timewarp number?

    DiskTech:

    ....aahhh, you're forgetting that regardless of whether you shoot 50i or 59.94i (assuming we're talking DV or HDV) the data rate doesn't change - it stays constant at 25Mb/s. The amount of data used in each field/frame is NOT the same when using 50i or 59.94i. Therefore - logically - if you play back material that is shot at 50i at a frame rate of 59.94, you are increasing the data rate by a factor of (approx) 1.2. Therefore you are no longer within the specifications of DV or HDV. Also, when you've created a timeline, you've specified the render codec for that particular timeline. That codec also specifies the data rate to be used so, when you place your 50i footage on a 59.94i timeline, you're "speeding up" the footage, but you also need to reduce the data rate by a factor of 0.83 in order to now reduce 59.94i frames of 50i data into a 59.94i data stream... It's one thing to come up with a magic number to create a 1:1 frame correlation - it's something else entirely to fit it withing the constraints of the various codecs....

     .....and if your talking DV as opposed to HDV, you need to realise that there are a lot of calculations going on as everything is resized from 720x576 to 720x480....

     Personally, I think that forty-two sounds like a blazing-fast number....   Stick out tongue

    Good point, that would explain the need to re-encode every frame, and I could buy that.

    By the way, I am talking about HDV because I agree the different frame sizes of SD PAL and NTSC would need lots of interpolationg/processing.

    But I'd like to continue this question -- what do you think would happen if instead of speeding up the data rate, a similar "conversion" was done that would slow down the data rate?

    My first example was not really what I'm ultimately aiming for -- it was just a test.  What I'd like to do is to first go from 50i to 25p with some kind of deinterlacing.  Then I'd like to drop the 25p video onto a 24p timeline and use the "magic" timewarp number that would be blazingly fast.  In this case, it should be slowing down the data rate.  Ultimately the final conversion would be to put the 24p video on a 60i timeline to get a "3:2" pulldown.

    The question then is: is there a magic timewarp number that would make the 25p to 24p conversion blazingly fast?

    I have heard mention that there might be a way to change the header of a 25p video file to make it a 24p video file without any reencoding.  So that essentially what I'm trying to achieve with the magic timewarp number.

    -SB

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