AVCHD Bitrate difference

brisa117

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Mar 16, 2010
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So I'm probably going to pick up my first DSLR soon. I've done my research and fell in love with the Sony A65 for both performance and price. I am also interested in using the camera for shooting video, and I really like the idea of shooting 1080p at 60fps. I'm not extremely familiar with bitrate, but I know the higher the bitrate, generally the better quality per frame. So I'm wondering which I would be better with: 1920 x 1080/60p@28Mbps or 1920 x 1080/24p@24Mbps.

By my calculations, that's 0.467Mbps for the 60p or 1Mbps for the 24p. At this point, I don't know if my final video output would be at 24fps or higher. I just know I would like to get the best image quality. Please, someone school me on bitrate here. I'm a huge PC nerd and know my fair share about video, but this is the first time I'm moving up to a higher end camera with these options.

Thanks in advance!
 

kenrivers

Splendid
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Not sure if this will help but it may be worth a read: http://community.ooyala.com/t5/Developers-Knowledge-Base/Understanding-Bitrate-Resolution-and-Quality/ta-p/1740
Looking at the specs I see if you wanted to shoot at 30fps it would HDV (1440x1080) so I guess that is not an option. As far as whether or not to shoot at 60fps or 24fps it would depend on whether or not there is a lot of motion in the scene. 60p would be better if there is a lot of motion or at least fast motion as you may get some motion blur if shooting at 24p.
 

brisa117

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Assuming this article know what it's talking about, which it seems to, I'll be in a good position with either. They say that a good bit per pixel (bpp) is 0.1 and that going above this won't produce a significantly better image. To figure out the bpp, we want to take the bitrate and divide it by the total number of pixels per second. Doing the calculations we find:



1920*1080@60p (28Mbps)

(28 x 1024 x 1024) / (1920 x 1080 x 60) = 29360128 bits / 124,416,000 px = 0.23598bpp



OR



1920*1080@24p (24Mbps)

(24 x 1024 x 1024) / (1920 x 1080 x 24) = 25,165,824 bits / 49,766,400 px = 0.50568bpp



Both of these bpp are well above the 0.1 "very good quality" standard. To me that means that each would be just fine. The article specifically says that your increase above the 0.1bpp won't result in significantly better quality, but I can't help but imagine I would get a better image from the 24p version which has over double the bpp. I suppose that will be a test for the field. In the long run, if the video is acceptably good quality at 60fps, I will choose that, simply because I can limit the fps in post processing and with 60fps I can also use some slow motion effects.

Thanks again for you help kenrivers!
 
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