Latest post Sun, Mar 3 2019 8:23 PM by Zak Ray. 6 replies.
Page 1 of 1 (7 items)
Sort Posts: Previous Next
  • Fri, Mar 1 2019 4:39 PM

    • Zak Ray
    • Not Ranked
    • Joined on Fri, Jan 28 2011
    • Posts 22
    • Points 260

    DNxUncompressed - is it really uncompressed?

    I see a lot of the literature around DNxUncompressed says that it's "visually lossless". To me, that implies some form of compression, no?

    Also, the FAQ says that 32-bit is currently supported. Does that mean 32 bit is the ONLY bit depth supported, or are lower bit depths currently available?

     

    Thanks!

  • Fri, Mar 1 2019 9:50 PM In reply to

    • jwrl
    • Top 25 Contributor
    • Joined on Thu, Oct 13 2005
    • Melbourne, Australia
    • Posts 8,387
    • Points 97,025

    Re: DNxUncompressed - is it really uncompressed?

    It will usually have to be converted from something, which involves a transcode unless you have media that was originally produced in that codec.  That conversion process inevitably results in losses, no matter how slight those losses may be.  Hence Avid have (wisely) used the term "visually lossless".

    MC 7.0.4 - Asus P6T Deluxe V2 mobo - Intel i7 920 2.66GHz - Windows 7 Ult64 SP1 - nVidia Quadro FX 1800 - 16 Gbyte low latency DDR3 RAM - Internal 8 Tb... [view my complete system specs]
  • Sun, Mar 3 2019 4:54 PM In reply to

    Re: DNxUncompressed - is it really uncompressed?

    Isn't this more an issue about changing the container rather than actually touching the content? Lower bit depths are usually supported but if you use them on content that has higher bit-depths then you're asking for what you're trying to avoid. As far as I know, because my workflow includes using the DNx codecs, what I do is shoot with an HMC80 set at its highest resolution (1920x1080x24p at the highest res) because it doesn't shoot RAW, then use the DNx container that matches those settings - then the content is untouched. Again, that's as far as I know. I like to consider these codecs as "preservation" codecs. The first thing I do is "preserve" the media from any loss by changing the container to DNx. I remember when I was in college one of my classmates used a 13" MacBook Pro and would get crystal clear timelines (he shot on a 7D) using ProRes codecs in Final Cut Pro 7 and 10 and I looked for an equivalent codec in Media Composer for PC. DNx was said to be the PC version of ProRes and so I began using it and got the same results my classmate got. I think I sometimes cause myself some issues because instead of letting the Avid pick the right one I go behind it and change the settings to the highest that raster and bit-depth allows. Huge files but I always get clean timelines to work with and clean exports. I have been told that when I do that I am adding dead data to the files because the HMC80 colorspace is 422 but I set the DNx codec to 444 (it's settings like those that make me say I think I cause myself some issues but I'm OK with it because again, my first objective is to preserve my media). If Avid is telling us a weasel then that weasel is the kind that is only harmful in that it has an element in it that toes the line between truth and deception because it sure doesn't cause any harm to what I have produced using it. In fact, one of the double-edged swords I am consistently falling on is how clean my projects are. Some people love it. Others will ask me to make it a little dirty.

    If my conclusions about DNx are flawed, someone please correct me.

    Machine 1: Custom 3.3GHz Intel Xeon E31245 QuadCore (8 threads, HyperThreading enabled) 16GB RAM (1666MHz) (set to 1600mHz) 2TB 7200rpm system drive (1... [view my complete system specs]
  • Sun, Mar 3 2019 5:23 PM In reply to

    • Zak Ray
    • Not Ranked
    • Joined on Fri, Jan 28 2011
    • Posts 22
    • Points 260

    Re: DNxUncompressed - is it really uncompressed?

    To my knowledge, the people saying that you're adding "dead space" are correct. If the HMC80 shoots 4:2:2, you're not gaining anything by going to 4:4:4 except extra file size. You certainly don't need the bitrate either, as the HMC80 caps out at 20 Mbps and DNx 444 is around 400 Mbps. Adding bits won't preserve your original any better. 

    If you're happy with your workflow then by all means keep it, but you'll be buying a lot of unnecessary drives.

  • Sun, Mar 3 2019 6:08 PM In reply to

    • jef
    • Top 50 Contributor
    • Joined on Sun, Feb 26 2006
    • Maryland
    • Posts 3,430
    • Points 41,355

    Re: DNxUncompressed - is it really uncompressed?

    Larry Smiley-El:

    Isn't this more an issue about changing the container rather than actually touching the content? Lower bit depths are usually supported but if you use them on content that has higher bit-depths then you're asking for what you're trying to avoid. As far as I know, because my workflow includes using the DNx codecs, what I do is shoot with an HMC80 set at its highest resolution (1920x1080x24p at the highest res) because it doesn't shoot RAW, then use the DNx container that matches those settings - then the content is untouched.  

    ......

    If my conclusions about DNx are flawed, someone please correct me.

    I do not really know much about the HMC80, but a quick Google shows it shoots AVCHD: MPEG-4 AVC/H.264.  A pretty highly compressed codec.  You say, "then use the DNx container that matches those settings - then the content is untouched."

    I would not use the word "untouched".  AVCHD and DNx are very different compressed codecs. To go from one to the other requires decompression and then recompression using a different systems.  This is where loss can definitely take place. I am just pointing this out so as to keep things straight.

    But your later write, "...I go behind it and change the settings to the highest that raster and bit-depth allows." I think most people here would agree that this is the most prudent path if you can afford it.  And your observations seem to have agreed.

    That said, I would agree with what some have told you that going all the way to DNx 444 is overkill.  You are not going to make up any "new" information in the process.  I would say going to the highest data rate 422 DNx would be fine.  The camera original AVCHD being a VBR low data rate codec has limited the quality the most.  Your goal for preserving it as best as possible would probably be well served with the 422 version.

    If you have access to After Effects or Fusion you could do a test between the 422 and 444 versions by Difference keying two identical clips (other than the codec).  This will tell you a lot about what is going on inside the codecs.

    Jef

    Avid DS 11.0.2 R.I.P | MC "Well, it depends ..." mostly 8.10.0 but playing w 2018.11| OS 10.11.x - various MacPro Towers - home system MacPro... [view my complete system specs]

    _____________________________________________

    Jef Huey

    Senior Editor

    Old Stuff  http://vimeo.com/album/3037796

  • Sun, Mar 3 2019 7:51 PM In reply to

    Re: DNxUncompressed - is it really uncompressed?

    The reason I started doing this is, I would sometimes notice degradation in my exports that I could not explain. The settings in my cameras did not change nor the settings in the Avid. I tried every single setting in the menus looking for what gave the best results and for whatever reason using the highest settings gave me the best results. I understand that AVCHD is highly compressed and that at this point (the point the stop button is pressed to stop recording) you are stuck with what you just recorded. When I let the Avid pick the DNx codec it picks different ones on occasion. That's why I started testing all of the settings. The ones it picked gave me mixed results and I absolutely hate having to sit there and try to figure out why one shoot is different from the other when I sat there to start editing - I just want to get it done. I want to go out and shoot. Bring it in and ingest it. Edit it. Color it. Export it. And then deliver it. I don't want the interruption of the rest of it that should have been dealt with when I set up my environment. So, I found the settings that give me predictably the best results and have stuck with them. I understand that I am not gaining anything by overcompensating. Gaining was never my intent. My intent is preserving what I captured. I carefully pick the projects I will crew and produce (I do a lot of live performance work and sports, along with a lot of studio shoots) and the one thing I pay close attention to is the lighting situation. The HMC80 IS highly compressing the files (AVCHD) BUT when you put those jokers in better than good environments, they shine like refined diamonds and I have really good control at the coloring stage when I control the recording environment. As long as I preserve what I shoot, and again the Avid changes what DNx codec it picks on occasion, and then overcompensate, I get exceptional results. At the least, I stick to the file as closely as possible because I was told that the Avid is an editor - not to be taken too seriously as a transcoder or anything else. So I DO try to avoid transcoding but sometimes that's not in the cards... At most, I overcompensate strictly to preserve what I captured because I have gotten mixed results otherwise and I cannot figure out why when the only media that is different is GoPro files and any b-roll that I didn't gather with the main cams.

    Hard drives? Oh my god, these files ARE killing me. However, I have learned the hard way to just tell clients "I need a deposit so I can get the supplies and hire the crew for this project." and see what they do. Some pay, some don't. Of course, the first thing I do is buy two drives - one to work on, the other one for backup.

    Machine 1: Custom 3.3GHz Intel Xeon E31245 QuadCore (8 threads, HyperThreading enabled) 16GB RAM (1666MHz) (set to 1600mHz) 2TB 7200rpm system drive (1... [view my complete system specs]
  • Sun, Mar 3 2019 8:23 PM In reply to

    • Zak Ray
    • Not Ranked
    • Joined on Fri, Jan 28 2011
    • Posts 22
    • Points 260

    Re: DNxUncompressed - is it really uncompressed?

    It sounds like your method is working for you and your clients, so I won't argue with it. To be clear though, putting the same amount of water in a bigger glass doesn't preserve it any better.

    If you were seeing degradation at the export stage, I'd say that's more likely an issue in your export settings. I would recommend choosing a modest DNx flavor (i.e. 145) for both your import and your export, then put your exported master files through another tool to create H264s or whatever you need for delivery.

Page 1 of 1 (7 items)

© Copyright 2011 Avid Technology, Inc.  Terms of Use |  Privacy Policy |  Site Map |  Find a Reseller