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Old November 12th, 2008, 05:43 PM   #1
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Help me understand Prores.

Help me understand Prores better and how or where is the best to use it.

I shoot on a Sony Z1, capture from camera edit HDV on timeline. I Do a bit of color correction using Magic Bullet and adjust levels, some fades, titles and lower thirds(supers).
I then would render out to mpeg-2 for DVD burning.
I have read so much about Prores I’m back to where I started… clueless
Why would I want to use prores/ what benefits would I see?

Nick
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Old November 12th, 2008, 06:24 PM   #2
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This question gets asked a lot, there should be a sticky thread for ProRes. Jason said it best so I'll just quote him.

Quote:
Originally Posted by Jason Livingston View Post
When working with HDV, the compression is done in the camera before the data is written to tape or outputted via firewire. The loss due to HDV has already occurred. When you transfer HDV to your NLE by firewire, there is no additional loss (just like copying a file bit-for-bit).

Pure HDV workflow:
When you put these HDV files on your HDV timeline with only cuts, there is still no loss because you aren't recompressing the data. The only time you get loss is when you have to make changes to the video, such as when using filters, titles, transitions, etc. If your timeline is set to render to the HDV codec, then any parts of your video that are changed will be decompressed, have the changes applied, and then recompressed in HDV (but other parts which are unchanged will remain in their full original quality). It is this recompression step that causes loss, since HDV is a pretty lossy codec. It also makes editing slow, because decoding and recompressing HDV is a lot of work for your CPU to do. The advantage of this workflow is that it uses the least disk space, and unchanged parts of the video incur zero quality loss. So this is a good workflow to use when doing mostly cuts-only editing with minimal rendering needed.

Mixed HDV/ProRes workflow:
If you use a HDV timeline but with the render codec set to ProRes, then this is what happens. Parts of the video which are unchanged will stay in HDV as they are without any recompression, so there is no loss. Parts that are changed will be rendered in ProRes instead of in HDV, which minimizes the loss. This workflow gives you most of the advantages of the pure ProRes workflow, but uses much less disk space (since your source files stay in HDV which takes much less space than ProRes) and doesn't lower the quality of unchanged parts of your video. The downside of this workflow (compared to pure ProRes) is that, since HDV is harder for your CPU to decode in realtime, you get slightly fewer realtime effects before needing to render. The upsides are that rendering is fast because ProRes is relatively easy to compress, you get minimal quality loss in changed parts of your timeline (and no loss in the unchanged parts), and the disk space required is only slightly higher than with the pure HDV workflow.

Pure ProRes:
The pure ProRes workflow involves transcoding the HDV data that comes over firewire into the ProRes codec, so the files on your disk are all in ProRes instead of HDV. Since ProRes is a (slightly) lossy codec, this means ALL of your video will LOSE some quality (although the loss will be pretty small). While it is true that ProRes is a higher quality codec than HDV, transcoding HDV into ProRes doesn't increase the quality, it only gives you the compression artifacts of HDV PLUS the artifacts of ProRes. This also requires a great deal more disk space, because ProRes uses something like 4-8x the bitrate of HDV. The advantage of this workflow is that since ProRes is easy for the CPU to decode and encode in realtime, you can have more realtime effects and faster rendering than with a pure HDV or mixed HDV/ProRes workflow. The downsides are that all of your video loses a little bit of quality and much more disk space is required.

So, in summary...

Pure HDV Workflow
Pros:
Least disk space
Zero quality loss in unchanged parts
Cons:
Noticeable quality loss in changed/rendered parts
Lowest realtime performance (both playback and renders)

Mixed HDV/ProRes Workflow
Pros:
Uses only slightly more disk space than pure HDV
Zero quality loss in unchanged parts
Minimal loss in changed/rendered parts
Cons:
Less realtime performance than pure ProRes (but faster renders than pure HDV)

Pure ProRes Workflow:
Pros:
Maximum realtime performance
Minimal quality loss in changed/rendered parts
Cons:
Slight quality loss in unchanged parts
Uses a lot more disk space
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Old November 12th, 2008, 06:35 PM   #3
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Thanks Pete,
Great post from Jason.
I wonder how much resoultion is lost in capturing prores.
I see some editors edit in HDV and then render out to prores, this is what I dont understand. Why would you render out to prores 422 if the next step is to encode for DVD?

Nick
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Old November 12th, 2008, 08:22 PM   #4
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Quote:
Originally Posted by Nick Stone View Post
I see some editors edit in HDV and then render out to prores, this is what I dont understand. Why would you render out to prores 422 if the next step is to encode for DVD?

Nick
It's not rendering OUT to ProRes, it's rendering dissolves, effects etc in the timeline to ProRes, which doesn't force FCP to "open up" an MPEG stream and recompress the stream (which if repeated becomes significantly lossy) like doing an HDV render does.
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Old November 12th, 2008, 08:44 PM   #5
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The other option is to transcode to Apple Intermediate Codec (AIC) upon capturing. Some people with better Apple post production knowledge than mine could explain to you the disadvantages of AIC as compared to ProRes apart from the format supported being much more limited. However, I can point out to you the advantages:

-Smaller file sizes than ProRes, thus saving you some disk space but still 3-4x the sizes of the original HDV footage

-Editing faster than ProRes, most Apple notebooks and iMacs can handle it very well with no issues.

-Transcoded clips or files can be exported to and edited in Final Cut Express and iMovie to save you time and money for certain tasks as both NLEs don't support ProRes.

I've done much of my work acquiring the footage in HDV and outputting the finished videos on SD DVDs using the AIC workflow and the results have been fine. I think compressing the final output (from AIC to MPEG-2) is more critical to the quality of the DVDs than the use of AIC or ProRes.

Someone may have a different view, though.

Wacharapong
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