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Old July 6th, 2007, 08:31 AM   #1
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HDV capturing...best quality???

Hi,

Please help......what is the best ( highest quality) capture that i could perform to get the best results from my mini dv HDV footage?

i-link dv(firewire) cable from camera? hdv video deck? capture cards? 10 bits capture?...aaarrhhh!

can someone clear the air for me?

many thanks.

Regards

T
Tristan Versluis is offline   Reply With Quote
Old July 6th, 2007, 02:09 PM   #2
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Well, it's easy.

Using firewire from your camcorder would be the same as using a deck. It could even be better from your camcorder because you'd be sure that the tracking would be perfect. Using firewire transfers data, so what you get is a perfect "clone" of your tape. No capture card can give you the quality of a digital data transfer.

You can use a specialized codec (like Cineform's AspectHD) to convert your footage to a format that is better immune to recompression in your editing software. For instance, using AspectHD in PremierePro (or cs2 or cs3) gives you a faster, cleaner editing experience.

Hope that helps a bit !
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Old July 7th, 2007, 11:21 AM   #3
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There are a couple issues here...

1. How best to transfer the footage without degrading it.
2. How to get the footage through edit without degrading it.

As to #1: The Firewire (iLink) transfer is, as Jocelyn states, a direct data transfer. You can't affect the footage quality in transfer this way as it is simply moving the bits.

Other options for ingest include coming in FW and transcoding to a different codec...I use the CineForm products (as Jocelyn also mentioned) and prefer this method. The footage is converted to the new codec, and therefore does undergo "processing"...but I've seen little to no quality loss in my subjective view. There are other options for "intermediate" codecs as well. One consideration for your situation is that the file size will increase with this method.

Ingesting using an AJA or BlackMagic card presents one more variable. These cards can typically handle HDSDI inputs, which in my case I can use my HD Connect LE to convert the FW output from my camera to HDSDI for my AJA LH card. The other option could be component analog, which most HDV cameras have at least options to do, and many of the larger I/O cards (AJA, BM again) can handle. The general idea with using these methods of ingest are that by decoding the HDV to the theoretic equivalent of digital "baseband" and sending the footage down the analog or serial digital pipe as effectively "uncompressed," some of the inherent artifacts in HDV footage may be "smoothed out" a bit. I know that the Convergent Design HD Connect LE box that I use makes quite a difference, but I've not tried the component analog route. For obvious reasons, when the footage hits the actual harddrive of the computer, it is NOT re-encoded into HDV, but is usually stored as uncompressed (for those with gargantuan storage), or some intermediate codec, again-CineForm comes to mind, and then output to some higher level HD format for mastering.



Now to #2: How to best edit HDV without degrading it.

The claim that was widely made by many NLE manufacturers is that if you are "cuts-only" on an HDV native timeline, there is no re-compression. This is unfortunately impossible, at least as far as outputting the timeline back to HDV is concerned. If we consider the factors of HDV compression of long GOP and CBR or constant (fixed) bitrate, and consider an edit sequence that might be considered typical in a broadcast or corporate environment:

(15 frame GOPs-Sony/Canon, assuming each cut represents new visual material)

Outpoint of first shot is frame 5 of the first GOP, the next shot's inpoint is frame 11 of the next GOP, so the edit looks like this in frame numbers:

1 2 3 4 5/11 12 13 14 15 1 2 3 4 5 6....

Even though the frame 11 in point is not an I-frame, due to the edit to completely new visual material, the frame must be reconstructed from the original GOP basically in its entirety, giving it the data size of an I-frame, even though it may be out of position within the original GOP to be an I-frame. With a 15 frame GOP, the fixed data rate of 25 Mbits/s is based on seeing a full-size I-frame every 15 frames...and we've just created three I-frames (in size at least) in 10 frames time. we are quite simply above the data rate allowable for HDV2 (JVCs 720p version of HDV is considered to be "HDV1" and uses a 6 frame GOP for frame rates up to 30, and a longer GOP for 60p), and the compression...and not just any compression, but very aggressive HDV MPEG compression, needs to further compress the video to keep it under the data rate ceiling.

This doesn't address the issue of I-frame shift before output, which happens when you output an HDV timeline back to HDV, but the I frames generated during acquisition have only a 1/15th of a chance of falling on an I-frame position in the output file....which results in recompression due to needing to juggle data and make predictive and bidirectional frames into I frames for output, while discarding most of the real image data contained in the original I-frames...

So...in a nutshell, I don't personally advocate editing HDV on an HDV "native" timeline if visual quality, or at least minimizing degradation is an issue.

Most intermediate codecs eliminate the long GOPs and other than DVC ProHD on the Mac, they also typically eliminate the fixed data rate, making the footage easier to edit by making the decode/encode steps easier on the processor. CineForm has the ability to bring the 8 bit footage into the system as 10 bit, making aggressive color correction an easier task.

Of course coming in as HDSDI or analog enables you to not only use intermediate codecs, but to also edit uncompressed. Uncompressed HD footage is oppressively large and does require much faster harddrives, though it's less taxing on the computer's processor because there is effectively no decode/encode steps...it's all about just moving lots of bits as fast as you can.

FCP has the potential (as do other NLEs) of using an HD uncompressed timeline, but editing HDV media. The uncompressed project settings keep any "re-compression" out of the picture until final output, even as the footage is being cut and manipulated, and the HDV media keeps the harddrive space requirements low.

...hopefully some of that is useful.
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Old July 7th, 2007, 01:25 PM   #4
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hi

thats allot to absorb....thank you to both of you.....Tim...could you suggest a workflow in FCP to prevent degrading?

many thanks again...

regards

tristan
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Old July 7th, 2007, 02:21 PM   #5
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I would suggest bringing in the footage via FireWire as HDV...

Then create a new timeline using uncompressed HD settings and edit on that timeline. You will only have to compress at the last step before you output, whether it be to SD DVD, MPEG4, or HDV...
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Old July 7th, 2007, 06:19 PM   #6
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Though I don't disagree with Tim's summary, I'm not sure that his last point is significant, even though true: NLE's only compress on export, so it is always true that compression is only applied as a final step ...

This has some implication for those that have a workflow that finds they often export a sequence and reimport it to put on the timeline -- that method would create multiple renderings. But otherwise, whether the material is on your timeline as HDV or as 'uncompressed' or an intermediate codec makes no difference.

Import using Firewire to get a bit for bit transfer, only export when you are 'done'.

Cheers,
GB
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Old July 7th, 2007, 07:01 PM   #7
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Quote:
Originally Posted by R Geoff Baker View Post
NLE's only compress on export, so it is always true that compression is only applied as a final step ...
The point is that an HDV timeline exports only to an HDV file...not the most popular option for mastering. An uncompressed timeline can go out to whatever you choose.
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Old July 7th, 2007, 07:07 PM   #8
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I'm surprized by that suggestion -- you can export anything from anything using any NLE I use ... your source doesn't determine your export options. Your mileage may vary, but I'd be curious what editor you use that has such a restriction?

GB
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Old July 7th, 2007, 07:19 PM   #9
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My thoughts are along the line of trying to output non-square PAR 1440x1080 HDV project to an HDSDI out...or an uncompressed HD timeline via FW to HDV?

I don't believe that FCP can output an HDV timeline via HDSDI without conversion to a conventional HD square PAR timeline setting...and maybe my experience is limited, but I've met very few people who are mastering to HDV.

The other issue is previewing effects and that sort of thing...which on an uncompressed timeline would be faster as encoding HDV MPEG2 is processor intensive...and necessary on an HDV timeline or in some other editors, with an HDV project setting.

Certainly you can output anything to anything...it's a matter of how many steps I suppose.

Anyone is free to do what they want...I'm just tossing out suggestions.
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