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Old 05-19-2017, 01:27 AM   #1
Megagoth1702
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Default Most "precise" video decoder? Sync issues!

Hey guys,

this is going to be nerdy and crazy technical, but I am a nerd and I like getting to the bottom of something as far as I can.

I have sync issues when importing video in REAPER.

I am working on a movie which was encoded with the Avid DNxHD Codec.

Code:
General
Complete name                            : D:\SomeVideo.mov
Format                                   : MPEG-4
Commercial name                          : DNxHD 36
Format profile                           : QuickTime
Codec ID                                 : qt   2005.03 (qt  )
File size                                : 2.93 GiB
Duration                                 : 11 min 29 s
Overall bit rate                         : 36.5 Mb/s
Encoded date                             : UTC 2017-04-06 17:21:08
Tagged date                              : UTC 2017-04-06 17:39:30
Writing library                          : Apple QuickTime

Video
ID                                       : 2
Format                                   : VC-3
Commercial name                          : DNxHD 36
Format version                           : Version 1
Format profile                           : HD@LB
Codec ID                                 : AVdn
Codec ID/Info                            : Avid DNxHD
Duration                                 : 11 min 29 s
Bit rate mode                            : Constant
Bit rate                                 : 36.2 Mb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate mode                          : Constant
Frame rate                               : 24.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:2
Bit depth                                : 8 bits
Scan type                                : Progressive
Bits/(Pixel*Frame)                       : 0.727
Stream size                              : 2.90 GiB (99%)
Title                                    : Apple Video Mediensteuerung / Apple Alias-Datensteuerung
Language                                 : English
Encoded date                             : UTC 2017-04-06 17:21:09
Tagged date                              : UTC 2017-04-06 17:39:30

Audio
ID                                       : 1
Format                                   : AAC
Format/Info                              : Advanced Audio Codec
Format profile                           : LC
Codec ID                                 : 40
Duration                                 : 11 min 29 s
Source duration                          : 11 min 29 s
Bit rate mode                            : Constant
Bit rate                                 : 320 kb/s
Channel(s)                               : 2 channels
Channel positions                        : Front: L R
Sampling rate                            : 48.0 kHz
Frame rate                               : 46.875 FPS (1024 spf)
Compression mode                         : Lossy
Stream size                              : 26.5 MiB (1%)
Source stream size                       : 26.5 MiB (1%)
Title                                    : Apple Ton Mediensteuerung / Apple Alias-Datensteuerung
Language                                 : English
Encoded date                             : UTC 2017-04-06 17:21:09
Tagged date                              : UTC 2017-04-06 17:39:29

Other
ID                                       : 3
Type                                     : Time code
Format                                   : QuickTime TC
Duration                                 : 11 min 29 s
Time code of first frame                 : 09:59:50:00
Time code, striped                       : Yes
Title                                    : Apple Zeitmarken-Mediensteuerung / Apple Alias-Datensteuerung
Language                                 : English
Encoded date                             : UTC 2017-04-06 17:39:29
Tagged date                              : UTC 2017-04-06 17:39:29
The video has audio embedded in it for syncing, it also came with an AAF for post production and when I import the video into ProTools, it syncs up nicely.

https://i.imgur.com/6b54ZXg.png

I exported the audio stems from PT, imported them into REAPER and then imported the video. It does not sync up. I played with REAPER's video decoder settings and when I use QT for decoding, there is a two sample difference between video-embedded audio and the audio stem.

https://i.imgur.com/zRwigpO.png

When I use my favorite decoder, vlc (it just works), there is a huge delay in the video's audio:

https://i.imgur.com/DiMf58i.png

Over 2000 samples!

So what's going on here and how can I fix it?

Interesting note - only the video's audio is affected. The test tone in the exported audio stem from PT starts exactly where the "test tone frame" starts in the video, no matter what decoder I use. The issue is with the audio here.


I appreciate any help and maybe this thread will help others too, once we found a solution.
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Last edited by Megagoth1702; 05-19-2017 at 02:21 AM.
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Old 05-21-2017, 08:17 AM   #2
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Damn, seems like this is too complicated? So no really reliable video sync in REAPER?
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Old 05-21-2017, 10:14 AM   #3
Bjorn218
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They may not be awake yet. I'm going to subscribe to this because I am having problems at the other end of video editing in Reaper. Seems every single render I do is de-syunched in a variable way. IOW the unsynchronized audio to video isnt a consistant rate leaving manual synching almost impossible. I have gone back to Shotcut for the time being and only importing a copy of the audio if I need to adjust it in Reaper
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Old 05-22-2017, 11:19 PM   #4
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Sorry for the rude bump. :O But I'm really, really curious if there is anything I can do to improve this situation.
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Old 05-23-2017, 03:33 AM   #5
heda
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I always have problems with vlc. I prefer ffmpeg, but latest builds are not working so well. But since you have a quicktime format with DNxHD codec you should use quicktime decoder and install the DNxHD codecs.
sometimes it is just better to reencode the file to a mjpeg quicktime or something that you know it works well.
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