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Converting 60i to 24p


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#1 Michael J. Murphy

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Posted 19 September 2006 - 06:09 PM

Hi-
I just started converting some of my footage from the HVR-Z1 (which, unfortunately, will not film in 24p) to 24p. As far as I know, I need to deinterlace the 60i video to get best results when converting to 24p. If I'm wrong, please correct me. Also, I understand that audio can get fairly distorted during the conversion and there's something I need to do to it to prevent the distortion. Again, the conversion process has left me completely confused. Can I have some guidance?

Thanks,
Mike
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#2 Brian Dzyak

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Posted 19 September 2006 - 07:46 PM

Hi-
I just started converting some of my footage from the HVR-Z1 (which, unfortunately, will not film in 24p) to 24p. As far as I know, I need to deinterlace the 60i video to get best results when converting to 24p. If I'm wrong, please correct me. Also, I understand that audio can get fairly distorted during the conversion and there's something I need to do to it to prevent the distortion. Again, the conversion process has left me completely confused. Can I have some guidance?

Thanks,
Mike



Isn't it really 59.94I and 23.98P? Let's start there...
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#3 Thomas Worth

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Posted 19 September 2006 - 08:08 PM

First of all, we need to know what method you are using for your conversion. For example, if using After Effects, what is basically happening is AE is deinterlacing the footage to 60p, then "picking" frames out of that to make a 24p version of the same video. Frankly, I feel this method is the absolute worst way to do it, but unfortunately converting 60i to 24p is not easy.

You can use frame blending in After Effects to minimize the "stutteryness" that results from the aforementioned procedure. But, that introduces other unnatural-looking artifacts (blurry motion). However, you might be able to live with them. I've seen plenty of footage shot 24p on a DVX100 with a 1/24 shutter. I don't like the look, but obviously others are okay with it.

If you have a Z1, a better plan would be to shoot PAL and convert that to 24p. This is a common procedure and works well. In almost all cases PAL footage converted to 24p is indistinguishable from material shot true 24p.
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#4 Michael J. Murphy

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Posted 19 September 2006 - 10:23 PM

Actually, I'm using Premiere for my editing. In the beginning I knew that shooting 50i would be easier to convert to 24p than 60i, but, unfortunately some of my to-be-24p video is already 60i. Luckily it is mainly for TV playback, so the conversion shouldn't be too noticeable. My other question is what I should do with the audio to avoid the well-talked-about distortion that occurs during the conversion process. What should I do there?

Thanks!
Mike
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#5 Tim Terner

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Posted 20 September 2006 - 01:42 AM

You could have a play with this http://www.dvfilm.com/maker/ there's a demo download avialable
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#6 Thomas Worth

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Posted 20 September 2006 - 02:22 AM

My other question is what I should do with the audio to avoid the well-talked-about distortion that occurs during the conversion process. What should I do there?

I'm not aware of any audio "distortion" with this process. Perhaps you are referring to the time discrepancy between the video and audio once 25p (PAL) footage is slowed to 24p for NTSC playback. This only affects PAL footage, not 60i NTSC footage being converted to 24p. The resulting video from a 60i to 24p conversion will have the same duration as the original 60i video. Therefore, no audio work is necessary.

Just for the sake of clarity, "distortion" would imply a mix level exceeding the maximum headroom of the playback device. With the PAL to NTSC 25p/24p conversion, the issue is not related to mix level -- it is simply an issue of the duration of the original audio not matching the new frame rate of the video. This is resolved by time stretching the audio to match the new frame rate (and therefore new duration). This can be done with audio software, preferably software employing a quality time stretching algorithm to retain as much of the original pitch / quality as possible.
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