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Film-out of HDCAM: How good is DNxHD *really*?
DNxHD for film out? DNxHD in general? Does the wonder of DNxHD break down when going from the tube to the screen? Perhaps, could DNxHD *improve* the experience? I’ve got an HDCAM show captured as DNxHD (well, oh, not true — yet — longer story actually — I won’t get into it here), editing Xpress Pro HD Mojo.
Several years ago, I color corrected and onlined Haskell Wexler’s Bus Riders Union, on the same system we offlined, Discreet Logic Edit 4.0. This was small budget, the CC primative. Analog RGB in and out, half the correction I did in the digitizing step by controlling setup, chroma et al on the BetaSP player itself. I had disk through-put issues, forcing me to bring the data rate as low as 250K for much of the film (top quality was 600K I believe).
But oh, the magic of TrueVision’s motion jpeg…. We did a Swiss Effects film-out to full frame 35mm Academy, which screened first at the DGA. The print was *amazing* looking. All I can think (besides the four weeks I spent tweaking the image and making sure NOTHING was clipped in the compressed space, at either high or low ends — I have no doubt the video master was far from broadcast safe — plus the care of Swiss Effects of the time) is that the TVMJPG codec was so nice, softened across detail so smoothly, that it actually improved the image for film by blending over video edges, blending away artifacting, while keeping a really crisp picture.
Now, this is all a stretch to apply to HDCAM and DNxHD… and 2005, I know. I tell the story here to suggest that mere detail and pixel accuracy (as in, of serial uncompressed versus compressed DNxHD or Cineform or… hey, TVMJPG) doth not the difference make … visually …. necessarily. So. Thoughts? Experiences? Am I a fool to think I can export a file from my DNxHD feature to CC and film-out, and have anything of quality?
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10 Replies
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Use DNxHD at the 220 rate. This will be far better than HDCAM. Master back to HDCAM-SR or HD-D5 for film-out. You should be fine on a film-out.
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com -
I did a test from DNxHD and uncompressed HD (both from a 2K scan) and did a film out and no one has yet been able to tell me where the split was done and which side of the frames are DNxHD and which are uncompressed. The output was viewed on both 35mm projection as well as 2K projectors from the original DPX output.
Michael
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Wow, so DNxHD is *better* than uncompressed standard HDCAM? I like to hear that. Is that true? I’m giddy. As far as the 220 rate, if I understand it, the equiv 10 bit rate is 175 when the frame rate is only 24p instead of 30i (?) — anyway, 175 is the top rate I see available in Avid for a 23.97p HD project. (Thanks for your reply)
“THE LOST SKELETON OF CADAVRA” –
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[BRussell] “Wow, so DNxHD is *better* than uncompressed standard HDCAM?”
HDCAM is NOT uncompressed. In fact it is HIGHLY compressed as well as prefiltered (high-frequency visual data is filtered out) before compression. So yes, in post, DNxHD (and other codecs, too) can achieve better results. Avid numbers their resolutions in various ways and not all DNxHD codecs are available on all of their HD-capable system. Here’s a link to their DNxHD whitepaper:
https://www.avid.com/resources/whitepapers/DNxHDWP3.pdf?featureID=882&marketID=
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com -
Thanks for the white paper. Yup (page 8) it seems 175 for 23.976p is the same top quality as 220 for the higher frame rate of 29.976. It would make sense, considering how HDCAM captures different frame rates — each frame is same chunk of tape signal regardless of rate.
In regards to HDCAM being not uncompressed (yes, isn’t it some kind of weird 3:1:1 at 135Mb/sec on tape?), but when you suck it out SDI, what’s written to disk is uncompressed. Wouldn’t then the post of this uncompressed stream, as media on harddrives, be lossless compared to DNxHD?
Indeed, such theoreticals are not stopping me. Proof is not in the theoreticals but the seeing (as in, heck, my TVMJPG experience). Based on your wisdom, it is clear to me that I can proceed this way. I intend to export the finished show to an uncompressed file to dump to SR or D5, or a computer at a film out company.
Thanks!
“THE LOST SKELETON OF CADAVRA” –
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[BRussell] “In regards to HDCAM being not uncompressed (yes, isn’t it some kind of weird 3:1:1 at 135Mb/sec on tape?), but when you suck it out SDI, what’s written to disk is uncompressed. Wouldn’t then the post of this uncompressed stream, as media on harddrives, be lossless compared to DNxHD?”
Numbers are funny things. The general concensus is that HDCAM is about 7:1 compressed based on the prefiltering. That has nothing to do with the 3:1:1 figure, which is the equivalent colorspace compared to 4:2:2. This is simply a ratio and Sony prefers to use the ratio of 22:8:8, while others say 3:1:1. All this means is that for every color-difference sample (:1) the luma is sampled 3 times (3:). In addition the codec is non-square (internal to camera and tape deck) with only 1440 horizontal samples versus the format’s 1920. Yes, when you go out of the deck via HD-SDI, the deck’s decoders are decompressing the signal back to full bandwidth HD.
When it gets into post, the codecs used will at the least have to not harm the image any more than the original codec. So theoretically uncompressed is better, but many codecs are visually or mathematically lossless. If you edited in a Sony linear bay for example, you would be going through multiple passes through the HDCAM codec as you do pre-read and other generation-adding edits. If you edit in an NLE, your choices are uncompressed or various codecs. In this case DNxHD stacks up quite nicely.
It all depends on what you are doing to the picture in post. The worst are keys and color-correction. Chromakeys are not that great with HDCAM, since the codec is pretty noisey to start with. That’s why a lot of effects work has moved to HDCAM-SR or even recording straight out of the camera head uncompressed to a hard drive array. Color-correction really taxes a codec, especially when you stretch gammas, increase color saturation, etc.
There’s certainly nothing wrong with uncompressed, but DNxHD is a good trade-off in quality and drive comsumption.
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com -
Thanks. It’s nice to feel educated.
So I guess HDCAM “cloning” at a place like Lightning Dubs isn’t really “cloning” (unless they do that propriety Sony thing instead of SDI, I don’t know what they do). The best would be to dub up to SR, and I’ll have to check that price. Anyway, sounds like even mild color pre-correction and other FX in Avid, with the DNxHD, is maybe something not to do, because loss starts to happen; but rather, export to 4:4:4 and stay uncompressed NLE (which I can do during online nearby, using FCP / Color Finese), or otherwise lay the finished show 4:4:4 export file to SR and work in a linear fashion at some studio? (This will all end in film-out.)
“THE LOST SKELETON OF CADAVRA” –
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[BRussell] “So I guess HDCAM “cloning” at a place like Lightning Dubs isn’t really “cloning” (unless they do that propriety Sony thing instead of SDI, I don’t know what they do). ….
…..but rather, export to 4:4:4 and stay uncompressed NLE (which I can do during online nearby, using FCP / Color Finese), or otherwise lay the finished show 4:4:4 export file to SR and work in a linear fashion at some studio? (This will all end in film-out.)”The Sony “thing” is SDTI. I don’t know if it’s proprietary or not as other companies have also used this technology. It bypasses the decode/encode and moves the compressed video across as data. Therefore it is true cloning IF that’s what they actually are doing. The Sony Xpri editor also uses this to move HDCAM native footage into Xpri.
There are a million ways to slice the pie. Since you are shooting HDCAM, I don’t know that you are gaining much with SR or 444 or anything else like that. I would suggest this route if you are concerned about it. 1) Capture and edit on Avid as DNxHD and apply no correction. 2) Output to HD D5 (better than HDCAM and more available than SR, for now). 3) Then book tape-to-tape correction in a daVinci 2K suite and master to HD D5 or SR for your film-out “electronic negative”.
This will be the fastest, most straight-forward route. You won’t be a guinea pig and will get the benefit of a good colorist at the controls.
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com -
So, would I be better off using DNxHD “175 x”, which is 10 bit, instead of “175” which is 8-bit (as in, better Avid filter and effects rendering?) Now, to be sure, right this very moment, I’ve rented a room and capturing the HDCAM tapes to SATA drives, DNxHD 175. I hear through the grapevine that Xpress Pro only does 175 and not 175 x, so I’m wondering if I’m taking a hit with that limitation.
Yes, I know I *should* do no filter or effects at all, instead should do what you said above (D5 to DaVinci)…. but, I might have to be a bad person and do some select mangling beforehand. Certainly, there are some After Effects special effects will be doing. Am I in trouble affecting DNxHD media in 8-bit environments (for media that will eventually go film-out)?
Thanks for everything, professor
“THE LOST SKELETON OF CADAVRA” –
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Don’t know. Theoretically 10-bit is better, but depending on your footage, you might not see any difference, since HDCAM is 8-bit to start with. As far as your AE effects, you’ll probably want to export uncompressed and do the effect that way and then import as either DNxHD or uncompressed. The workflow will depend on which Avids or other NLEs you have at your disposal. Although AXP can work with HD today, I really think you should use it as an offline tool and then see about something more advanced for final conforming, like DS and Symphony Nitris.
Sincerely,
OliverOliver Peters
Post-Production & Interactive Media
Orlando, FL
http://www.oliverpeters.com
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