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Old October 21st, 2011, 03:15 PM   #1
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HD AVCHD Video Compression/Frame Rate Question

I don't know if this is the right place to ask this question? It might even be 'the stupid question'.

I don't understand the differences between the following compression formats and frame rates, nor do I understand what advantages, or the practical uses of each may be. The simple question I suppose is, "Why would I choose one over the other and what shooting scenarios would I choose one over the other."

1080/60i@24Mbps
1080/30p@24Mbps
1080/24p@24Mbps
720/60p@24Mbps

I sort of understand 'interlace & progressive' scanning systems and 'progressive' is preferered.

Please type slowly, you're dealing with a 'Noob'.

Regards,

J.
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Old October 21st, 2011, 08:44 PM   #2
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Re: HD AVCHD Video Compression/Frame Rate Question

Hi James; this may be "the blind leading the blind", but happy to say what I can. Others will surely add more..

As you can appreciate, 1080 will be a higher resolution than 720; the picture should be clearer and crisper. If your eyes can make it out that is - many people just can't see the difference.

60i is the US version of interleaved video. (It's 50i in PAL-land). So you are seeing 60 half-frames, or 30 full frames, per second. Because of the infinitesimal time differences in field capture, and the phenomenon known as "persistence of vision" in the human eye, we tend to see the result as fluid motion. This is referred to as the "video look".
30P shows you 30 progressively scanned frames per second. That is good from a presentation point of view - clear images - you can get some "juddering" - this is even more marked if you go to 24P - this is the "filmic" view. Movies you see in theatres are shown at 24 fps; if you look carefully when the camera pans sideways you can see "afterimages", because your eye is still registering the previous image, and the new one has moved a bit. Some people like this, they say it's filmic and professional etc. I personally prefer the smooth motion of video.

The AVCHD standards for compression and bitrates dictate that you can have interleaved video 1920x1080 at 60i. If you want to go to 60P (60 progressively scanned frames per second - this gives you the best of both worlds - clear images AND fluid motion) you can only have 1280x720. As of July 1 this year however, the standards were expanded to version 2 AVCHD - bitrates of up to 26 Mb/sec are OK, and this will support 1920x1080 @ 60P (or 50P). As yet I have not seen hardware (Bluray players/recorders) that are compatible with the new standards, but they will come.

What should you choose? Hmm - ask 20 people and you will get 20 answers :). Personally - go for the highest resolution you can. (1080). Interleaved video will give good results especially when there is faster action - less juddering. Of course if you have the opportunity 1920x1080@60P solves all your problems...
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Old October 21st, 2011, 10:31 PM   #3
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Re: HD AVCHD Video Compression/Frame Rate Question

Ron...that's as good of a description as I've seen. I plan on buying an Sony HXR-NX5U, it supports numerous compression/frame rate formats. I've 'read' one of the best settings, the wedding videographers like is 720/60p for 'slow-mo' affects. The 'NX5' supports 1080/60i, 1080/30p, 1080/24p, and 720/60p (all @ max. 24Mbps). These are not the only compression/frame rates the camera supports, but these are the HD formats with the highest bit rates.

I'm just trying to wrap my head around the basics, anticipating that I'll deviate from the 'norm' as I gain more knowledge and a personal artistic flair.

If you, or anybody else have 'suggestions' or shooting style recommendations using the afformentioned formats please feel free to voice your opinions. I've discovered, like a lot of things in life, there are no hard and fast rules, but I also know that the DVi collective wisdom is extensive and most are willing to share their experience. I thank you.

Take good care of yourself,

J.
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