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-   -   Importing 16 bit audio from video to a 24bit session is 1/4 frame early (http://duc.avid.com/showthread.php?t=404724)

Led 05-15-2019 04:25 AM

Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
Hi, I've noticed for ages with omf's and accompanying video from one place I do work for that the guide audio on the pics and the omf are about 1/4 frame out of sync, with the audio from the video being early. Today I noticed that their guide audio on the pics is 16 bit I spent some time exporting counters and pips out of Resolve at 16 and 24 bit, and when I pulled the 16 bit version into a 24 bit session, same thing occurred. I used to think it was related to Premier but it seems to be caused by the conversion to 24bit on import.

Has anyone else noticed this, or as I assume you probably always get 24bit guide audio on pics you receive?

If anyone else has had it, have you found it's resolved in one of the later versions? I'm on 12.5/Win10, but it happened on another system running 12.8, I haven't got 2018 to try it on.

I know a solution is to just ask the editors to always run 24bit audio but it's not always possible to know somethings coming far enough ahead of time. They may have a reason for doing it 16, I haven't had a chance to talk with them yet.

Leverson 05-15-2019 06:54 AM

Re: Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
What kinds of video codecs are you receiving? And what kind of audio with them? I find that often when I receive H.264 video encodes they are about a quarter frame off sync with the guide audio. Even if I reconvert to ProRes the offset remains. I had assumed it was a factor in the H.264 encoding process as it's an inter frame codec and things get sloppy, or part of the AAC or mp3 audio convert that tends to go along with them. I've never thought to test to see if bit rate is also a factor.

Either way, good rules of thumb are 1.) trust the sync of the AAF/OMF audio over the video reference guide track, and 2.) When head and tail pops are exactly a frame just slip the video guide audio track over until the beep boundaries are back to exactly within the frame alignment again.

KingTor 05-15-2019 08:50 AM

Re: Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
Quote:

Originally Posted by Led (Post 2525790)
I used to think it was related to Premier but it seems to be caused by the conversion to 24bit on import.

Me, too, until about 2 minutes ago. ;)

Thanks for tracking this down. If the whole guide track is off and there is a sync pop/pip/piep, I suppose the best solution (short of a different export) is to line up the pop with the frame edge on the video.

As for the follow-up post, I can't reliably use h264 from Premiere even after transcoding, and have found the best output from Premiere to Pro Tools to be an mxf wrapper around the Pro Res codec. I'd have to check to know whether or not that solved the OP's issue.



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Led 05-15-2019 02:42 PM

Re: Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
Quote:

Originally Posted by Leverson (Post 2525810)
What kinds of video codecs are you receiving? And what kind of audio with them?

They send H264 mp4 which I transcode in Davinci Resolve (which the free version is great btw) to DNxHD as a mov. The result has always been the same with both once imported into PT, but when you drop on the timeline in resolve and it doesn't match the program settings, it asks if you want to change settings to match the video, which I always say yes to. This sets up the export to default at the same bit depth as the imported video. So I've been exporting DNxHD with 16 bit audio. Now that I worked out the issue, I exported a previous video at 24 bit and imported it and the guide audio was in sync.

I'll have to check on Resolve but the audio in all cases I'm pretty sure was linear pcm. I wonder if the issue exists with 16 bit audio only files as well...today I'll export pip tracks only and have a look.

Led 05-15-2019 02:46 PM

Re: Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
Quote:

Originally Posted by KingTor (Post 2525847)
Me, too, until about 2 minutes ago. ;)

Oh my god, this has driven me nuts for about 5 years. I do a lot of TV for these guys, and it's always there, but another prod house I work for uses Premier as well and their stuff is always fine.

tom_lowe 05-21-2019 01:00 AM

Re: Importing 16 bit audio from video to a 24bit session is 1/4 frame early
 
Quote:

Originally Posted by KingTor (Post 2525847)
.

As for the follow-up post, I can't reliably use h264 from Premiere even after transcoding, and have found the best output from Premiere to Pro Tools to be an mxf wrapper around the Pro Res codec. I'd have to check to know whether or not that solved the OP's issue.

I’ve never seen an option to put ProRes in an MXF in Premiere Pro, only DNxHD/HR amongst others. Where’s the ProRes option?


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