Levels shift in DNxHD QT to DNxHD QT output

[seanmc]

I am starting out with a DNxHD mov output from an Avid. The export was from an edit with a DNx175x video mixdown, exported "same-as-source" at 709 levels. I want to rewrite this file using ffmbc.

I used this command line:

ffmbc.exe -i source.mov -s 1920x1080 -vcodec dnxhd -timecode 00:59:58:00 -vb 220000000 -r 23.976 -acodec copy output.mov

I would assume that the output file should match the input file as far as video levels go but it does not. The source has it levels in the native 16-235 range and output file appears to be 0-255 levels.

How can I get the output to match the 709 levels of the source?

[bouke]

----- Original Message -----
From: "seanmc" <se...@goldeneraproductions.org>
To: <ffmbc-...@googlegroups.com>
Sent: Monday, November 05, 2012 7:16 AM
Subject: [ffmbc-discuss] Levels shift in DNxHD QT to DNxHD QT output


>
> I am starting out with a DNxHD mov output from an Avid. The export was
> from
> an edit with a DNx175x video mixdown, exported "same-as-source" at 709
> levels. I want to rewrite this file using ffmbc.
>
> I used this command line:
>
> ffmbc.exe -i source.mov -s 1920x1080 -vcodec dnxhd -timecode 00:59:58:00
> -vb 220000000 -r 23.976 -acodec copy output.mov

Why re-encode if it's already DNxHD? A -vcodec copy would be faster and
retain all original info.
That probably won't help you, as i suspect the QT wrapping to be the
culprit.

> I would assume that the output file should match the input file as far as
> video levels go but it does not. The source has it levels in the native
> 16-235 range and output file appears to be 0-255 levels.

I'm having the same issues (will start a new thread about that) on Prores
encoding.
However if i transcode to DNxHD it's all fine...
What do you use to look at them and see they're not correct? (Don't use FCP
/ QT to show you correct levels...)
What does a fast import / ama link in Avid show?

Bouke

[se...@goldeneraproductions.org]

Why re-encode? Slightly long story but the gist of it is I am encoding a number of video files for use in Blu-ray authoring. I am using x264 to do the encoding. x264 can source from the DNxHD QT for this. The problem is that x264 is picky about the source QT. If the Avid timeline has mixed codec material and a same-as-source export is done to a self-contained MOV file, the result in x264 is a freak out and an encode full of digital noise. If the QT from the Avid was exported same-as-source from a timeline that had a solid video mixdown, all one codec, then x264 produces a very nice looking encode.

The DNx QT exports I am working with were done a couple years ago and a few of them have some mixed resolution material in them. I can open one in QT and re-export it as a DNx175 MOV and it produces a clean MOV with one solid codec all the way through and it matches levels and color exactly to the source. The problem is that doing it through QT is very slow. I was hoping to use FFMPEG to do this as it is much faster but I am running into this video levels problem...

I am using Adobe After Effect to pull both MOVs into a timeline and compare them as layers. I did a test encode through x264 and this is showing the same levels problem.

-Sean