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Why Transcode 50MB/s C300 MXF to ProRes?

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Misha Davia
Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 12:00:43 am

Hi everyone,

I have been told before when working with 7D footage and other low bitrate formats that transcoding to ProRes 422 HQ, or even sometimes just ProRes is a waste of hard drive space since transcoding to ProRes simply balloons the data rate of the original footage without adding quality.

I am wondering why this is not the case for C300 footage. With its data rate coming in around 50Mb/s, why is it recommended to transcode to ProRes 422 or ProRes 422 HQ when editing in Final Cut, or when delivering? Obviously you can't make the quality better than the original 50mb/s file so what is gained through going to ProRes? Just something I'd like to understand... thank you!


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Shane Ross
Re: Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 12:14:13 am

FCP 7 doesn't work with the format the camera shoots. It doesn't work with MXF files. You need to convert it to ProRes Quicktime files because that IS a format that FCP 7 works with.

FCP 7 doesn't work with H.264 either...thus why you convert that too. There is a list of formats that FCP 7 works with...those are found in the EASY SETUP list. H.264...and XDCAM MXF...are not among them.

Now...the C300 shots XDCAM 422 in the MXF format. it's an 8-bit codec, but a good one. I'd still convert to ProRes 422...not HQ. HQ is meant for 10 bit camera original formats like RED or Alexa.

And yes, there are plugins that allow you to edit the MXF format in FCP 7...such as Calibrated or MXF4Mac. But the format won't edit smoothly...the system will be bogged down. Why? Because the XDCAM 422 format is Log GOP, and complex...and FCP 7 is 5 years old, and a 32bit app, and just not the best option for editing this format native.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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David Roth Weiss
Re: Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 1:55:47 am

In addition to what Shane wrote, the Pro Res codecs are referred to as nearly lossless, high-performance codecs, meaning they are very high quality, but NOT processor intensive codecs (such as h.264 and other MPEG variants) that require high level computations. So, they playback easily and seamlessly on virtually any system, and without big and beefy hard drive subsystems.

David Roth Weiss
Director/Editor/Colorist
David Weiss Productions


David is a Creative COW contributing editor and a forum host of the Apple Final Cut Pro forum.


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Roger Poole
Re: Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 12:00:43 pm

In addition to what has already been said. Long GOP formats don't have the same frame structure that we are used to, F-F-F-F, it's composed of I - B and P frames. GOP, or Group Of Pictures interact with each other and in a sense have a life of their own. Difficult to work with as it was never designed as an editing format. Converting to ProRes makes it all I frames, F-F-F-F, like a film strip. Very high quality, easy to work with and easy on the brain.


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John Rofrano
Re: Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 1:50:42 pm

...and just to expand on why you should not be editing Long GOP formats you need to understand how the Group of Pictures are processed. As Roger pointed out, instead of every frame being a full frame of information like ProRes has, Long GOP formats usually use a 15 frame group. That means that 1 out of every 15 frames is a full image (I-Frame). The other 14 frames are delta frames (B-Frame) and predictive frames (P-Frame). These frames only store what is different from the previous frame. This is known as inter-frame encoding where frames have interdependencies on each other. What this means is if you park your playhead on the 14th frame of a 15 frame group of pictures, your computer has to process the 13 frames that came before it in addition to the 14th frame to display that one frame! That's a LOT of processing! By contrast, if you park the play head on any frame in a ProRes file (which uses intra-frame encoding), all your computer needs to do is read that frame and display it. Much easier. You want to edit with intra-frame codecs and not inter-frame codecs.

So editing Long GOP formats is an extremely processor intensive task and you don't want to be doing that unless your software is specifically designed for these formats (i.e., it's caching frames because they are expensive to recreate) and you have a powerful processor. As others have pointed out, ProRes eliminates these problems by converting every frame to a full frame so that it can be edited easily and accurately. Of course this increases the size of the file because full frames are being stored instead of partial frames but that's a small price to pay to make editing a lot easier.

Also as others have pointed out, FCP 7 requires you to use ProRes for formats that it doesn't support. FCP X will edit most of these Long GOP formats natively and if you have a modern Mac it should perform rather well. So using old software with new formats comes at a cost... i.e., you need to transcode to make it work.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Roger Poole
Re: Why Transcode 50MB/s C300 MXF to ProRes?
on Jun 20, 2015 at 2:44:47 pm

Excellently explained John. It makes my head hurt just thinking about it.


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