ProRes Bit Rate Question.

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Bill Rich

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ProRes Bit Rate Question.

PostSat Mar 30, 2013 2:14 am

I was just test grading recent rushes I shot for an upcoming mini-doc I'm shooting with my BMCC in ProRes Film log.. and checked the data rate on the clips in FCP7 and it's only showing 26.5MB/s. is this right?
My GoPro rushes are showing over 36MB/s.. I thought the camera is supposed to shoot around 220MB/s.. Am I doing something wrong?
I copied the files off the SSD onto an External drive same as I do with rushes from all my other cameras.. I'm importing the clips directly into FCP7..
What am I doing wrong here?

EDIT: I just imported a clip I just shot directly from my SSD and it's still only showing 26.5 MB/s.

Is anyone else seeing this from their ProRes clips in FCP7?(or any other NLE?)
Bill Rich
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Trevor Zuck

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 4:20 am

How big is the file and how long is it?
- TZ

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Tom

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 6:36 am

Over the years I have noticed how unreliable bit rate tags were for files on both mac and pc. Best thing to do is to load it into something like quicktime or vlc and check the movie inspector, it can be a bit more accurate.

Also, ensure you are not confusing Mb/s for MB/s
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FredP

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 6:46 am

Bill,

ProRes shoots at 220 megabits (220Mb), and the tag you're looking at is saying 26 megabytes (26MB). Lower case "b" is for megabits, and upper is megabytes.
Last edited by FredP on Sun Mar 31, 2013 4:56 pm, edited 1 time in total.
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Peter J. DeCrescenzo

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 7:31 am

ProRes is a variable bit rate codec. The actual bit rate in a ProRes recording varies depending on the recording format (FPS & resolution) and a scene's content.

The BMCC can shoot "ProRes 422 HQ" which has a target data rate of up to about 220 megaBITS/sec for 1080p30 (10-bit 4:2:2). The camera's other frame rates result in slightly lower ProRes target data rates.

(I believe it's a similar situation with the flavor of DNxHD that the BMCC shoots.)

Attached are excerpts from Apple's "ProRes White Paper"; the full document can be downloaded here:
http://www.apple.com/finalcutpro/resources/

prores data rates p0.jpg
prores data rates p0.jpg (63.92 KiB) Viewed 5120 times

prores data rates p1.jpg
prores data rates p1.jpg (95.88 KiB) Viewed 5120 times

prores data rates p2.jpg
prores data rates p2.jpg (107.13 KiB) Viewed 5120 times
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Bill Rich

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 11:20 am

Could someone else that has a BMCC and FCP7 tell me what data rates they are seeing from the BMCC ProRes clips? (or any other NLE that display that info?)

I appreciate all the replies..

I was shooting 1080/29.97 so according to the charts I should be around 220 Mb/s

So what I'm looking at is this..
the BMCC clips are showing 26.5 MB/s my GoPro 3 clips are 36 MB/s.. and other clips provided to me shot with a GH3 from an external recorder in ProRes is showing 50 MB/s..

I might be reading all this wrong.. but it seems to me that the BMCC clips should be displaying a higher data rate than a gopro and GH3 pro res files.
Bill Rich
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adamroberts

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 2:50 pm

Was the GH3 and GoPro footage 30p or 60p? If 60p then I'd expect the bite rate of transcoded footage to be higher than the BMCC.

The data rate for the BMCC that you have listed is about right.

BMCC shoots 220mbps when shooting 30p. That is 27.5MB/s. Pretty close to your 26.4MB/s you have listed in FCP7.
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Bill Rich

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 2:59 pm

Thanks Adam and everyone for easing my mind about this.. it makes sense now..
Yes the GoPro was transcoded to ProRes 422 and was shot at 1080/60p and the GH3 was actually recorded externally into ProRes..

The BMCC clips are still great looking!
Bill Rich
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Trevor Zuck

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Re: ProRes Bit Rate Question.

PostSat Mar 30, 2013 6:20 pm

FredP wrote:Bill,

ProRes shoots at 220 megabits (220mb), and the tag you're looking at is saying 26 megabytes (26Mb). Lower case "m" is for megabits, and upper is megabytes.


No the "M" is always capitalized. Mb = Megabit, MB = Megabyte. The capitalization of the "b" signifies bits or bytes.
- TZ

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FredP

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Re: ProRes Bit Rate Question.

PostSun Mar 31, 2013 4:55 pm

TZuck,

Oops, you're quite right. Teach me to try and send a message from an iPhone while in line at a StarBucks. Not really paying attention.

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