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Best Settings for transcoding .mkv to DNXHD

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Tom Carlson
Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 4:31:12 pm
Last Edited By Tom Carlson on Jul 21, 2016 at 4:31:59 pm

I have a transcoding question:

I'm doing some work restoring a musical film score and would like to be looking at the picture as I work in Pro Tools to check sync. I've transferred the video from a Blu-ray disk and now have an MKV file. What I would like to know is what are the best quality settings to use to transcode to DNXHD? Here are the specs of the source:


This is really just an intellectual exercise, rather than a practical one, as I will most likely transfer to DNXHD 36 and call it a day, but I'm curious at what point one wouldn't gain any quality. So, would the truest match to the original be:

Codec: DNXHD 175--8bit (or would 10 bit be better-looking even though coming from a compressed source?)
Frame Rate: 23.976 (that is the rate of the original)
Key Frames: Auto
Frame Size: Same as Source
Color Level: ??? RGB or 709?
Alpha: None
Stream Type: ??? Non-Streaming (Not Hinted)? or Streaming (Hinted)?
Audio Codec: PCM Linear
Channels: 5.1
Sample Rate: 48K
Bit Depth: 24 bit
Endian: ??? Little or Big? (I'm working on a Mac)

I believe that is everything. I'm particularly ignorant about Color Level, Stream Type and 8 or 10 Bit when coming from previously compressed sources (Blu-Ray).

Thanks in advance for your help!

Tom



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Michael Phillips
Re: Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 8:16:25 pm

It's always difficult to create a direct mapping of LongGOP enoded material with I frame based codecs such as MPEG and DNxHD. Also, is it for reference only, or will it need to be rebroadcast, re-encoded, etc. are all questions we face when using MPEG encoded sources. In your scenario, DNxHD 36 is more than enough for reference. Since sources is most likely 8 bit, the next higher quality would be DNxHD 145. Anything beyond that starts to be overkill.

DVD and BlueRay encoded material follow broadcast specs, so it will be Rec 709 for the HD version.

Again, for picture reference in your situation to check sync, DNxHD 36 will be a good balance overall other than a higher data rate H.264 type file.


Michael


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Tom Carlson
Re: Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 8:49:42 pm

Thanks so much for that information, Michael. Yes, for reference only, but I always like to know what is possible to improve quality, because one never knows what will be asked for next.

I've noticed one thing is that the film tends to stop one frame every second or so. It reminds me of when we used to look at NTSC footage on a Pal rig where they just repeated the 24th frame...or was that the other way around? At any rate, once a second, it's almost like an extra frame has been added so the motion isn't as smooth as it could be.

I found the motion was slightly better overall using Photo - JPEG, which is a very old trick from back in the SD days. But not enough to make a big difference. All in all looks rather crap anyway compared to how the Blu ray title looks on an HD TV, but that is to be expected, I suppose. I'm thinking the jerkiness might be more of a QuickTime issue or Pro Tools issue than a transcoding issue? Both QT and PT have the same playback issue, particularly noticeable on panning or tracking shots. Playing back from an SSD Raid and using an NVIDIA Quadro K5000, so I think those should be adequate. However, I am still on a mid-2010 Mac Pro (5,1) 2.93 GHz 12 core, so maybe that has something to do with it?

The original-original source was an animated film from 1997, for which a Blu-ray master was made just a few years ago. I could probably go to the studio and get an output of something for my ref, but that would be a hassle for something that is really just a convenience. For now, the DNX HD should be absolutely fine, unless you know of a way to change the settings in Squeeze Pro so that the final output plays more smoothly.

Thanks again!



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Michael Phillips
Re: Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 10:11:42 pm

The frame skipping or duplication once a second sounds like a bad frame rate conversion between 24.000 and 25.000 frame per second. Typically US DVD content that is 24.000 theatrical or 23.976 intended for broadcast is encoded as native 23.976 on disc in order to save space, increase the quality (higher data rate due to fewer frames), and has flags to let the player create the 2:3 pulldown.

At this point, you are never going to get better quality, but are looking to preserve existing quality as much a possible. I wonder if the source frame rate on your MXV is anything but 23.976? In Media Composer, I would AMA link to the source in a 1080p/23.976 project, and set source settings to project rate to ensure it was 23.976, then step through the media frame by frame to check. Then from there, transcode to DNXHD 36 and export QuickTime SaS. The Drastic Technology MediaReactor AMA plug-in supports MXK as an input.

Michael


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Tom Carlson
Re: Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 10:23:25 pm

Great. I'll give that a shot and let you know if it turns out any better.

I would assume that using the Avid to do the conversion would be better than ffmpeg or Sorenson Squeeze? If only for the GUI?

Tom



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Michael Phillips
Re: Best Settings for transcoding .mkv to DNXHD
on Jul 21, 2016 at 11:27:19 pm

Mainly it's because I know well and can track the frame rate easier on source versus delivery. But if you have MC, then give it a shot. The ability to change source rate when AMA linking started with v8.3.


Michael


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