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Nick Bedford

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  • Joined: Wed Aug 22, 2012 3:56 am
  • Location: Brisbane, Australia


PostWed Aug 29, 2012 9:49 am

Well, the Canon C100 was just announced, and it's rumoured to cost something like $8,000. The funny thing is, it's internal recording format is 24mbps AVCHD 4:2:0. Hell, even my 60D records video at about 40mbps (H.264), and that has issues. It can record in C-Log, which I would have thought 24mbps compression to chew to death, considering log compresses dynamic range and would result in banding.

It makes me glad that a company like Blackmagic Design exists. They get it. They get that to colour grade and to have a sharp solid image, you can't compress the hell out of it and blow away all the resolution by shoving it into a low bit-rate, under-sampled codec.

Bring on the 10-bit 184mbps ProRes 422 HQ! (and obviously raw!).

**thank you with the bottom of my photographer's heart**
Nick Bedford, Photographer
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Dylan Reeve

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  • Joined: Thu Aug 30, 2012 9:21 am
  • Location: Auckland, New Zealand

Re: Codecs

PostThu Aug 30, 2012 11:58 am

Simply comparing numbers isn't usually very helpful when evaluating codecs. What's far more important is the efficiency of the encoders.

AVCHD is basically an H.264 variant - it's directly comparable to the H.264 that Canon's DSLR's record but even then comparing the bitrate isn't helpful. The Canon DSLRs use such a high bitrate because they aren't optimised for video compression. Rather than use a lot of processing power to compress the image well to 24Mb/s they instead do a quick and dirty compression but use a high bitrate to compensate for it.

By rights an H.264 stream at 40-50Mb/s should be pristine - that is a LOT of bandwidth for a codec like H.264, but because Canon had to optimise for speed in their implementation they don't compress the video very well and end up a higher bitrate for what could be achieve with much less.

As for AVCHD at 24Mb/s - generally that's likely to conform to what Panasonic calls AVCCAM and what Sony calls NXCAM. It's a fairly high bitrate (for AVCHD) with a high efficiency encoder. Most people would consider that it delivers a better quality than Sony's XDCAM EX (MPEG2 4:2:0 at 35Mb/s) and that was apparently good enough for their $20k PMW-F3.

Blackmagic are taking a different approach by offering either a reasonably usable raw recording (although the file size is huge and post is currently difficult) or a widely supported NLE-native codec in either ProRes or DNxHD. This is practical because they're usual SSDs for recording, but that has it's own drawbacks.

There is no one best camera. They all have a whole range of pros and cons and need to be evaluated within the context of their use. There are plenty of ways in which the Blackmagic camera will fail to meet the needs of some users and applications.

Try to look at the bigger picture with all these cameras, they each are built with a specific ideology and will fit different needs in different ways. Just looking a numbers (bitrate, sensor size, whatever) will just mask the really useful details.

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