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Audio out of sync when m4v file played or Roku


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#1 Gilgamesh_48 OFFLINE  

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Posted 07 April 2020 - 07:48 PM

Server beta ver 4.5.0.4

Roku beta ver 3.0.219

 

I just happened to have a very few m4v files in my files system. As most know these are basically mp4 files so "should" direct play on virtually everything. However they are transcoded when playing on my Roku. The audio is two or three seconds ahead of the video but when I force direct play or play them on devices that direct play m4v the audio syncs correctly.

 

I will attach a couple of files so you can test.

 

I ran the files through "FFmpeg Batch AV Converter" to produce mkv files and those mkv files play perfectly.

 

I no longer have the misbehaving files in my Emby directory structure but I can created a temp library and move a couple into that and produce a log file if needed.

 

Thanks.

 

Apparently the file did not attach. I will try again.

It failed again. I get no error but I will try another way.

 

This is a DropBox link to the file

https://www.dropbox....oo Far.m4v?dl=0


Edited by Gilgamesh_48, 07 April 2020 - 08:32 PM.


#2 Luke OFFLINE  

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Posted 07 April 2020 - 10:14 PM

Did you explore the stats feature to learn why they were not direct playing?



#3 Gilgamesh_48 OFFLINE  

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Posted 07 April 2020 - 10:36 PM

Did you explore the stats feature to learn why they were not direct playing?

Nope I do not really know what the "stats" feature is or how to use it.

 

I have discovered something new, or at least different: If any file that is misbehaving is played directly from the file system using VLC it plays fine but if you use Windows Media Player or play it through Windows' Movies and TV functionality then the sync problem is there.

 

But like I said once I converted it to an mkv using "FFmpeg Batch AV Converter" the files all play perfectly.

 

I am not really sure how important this is. When I searched my file system I only found 7 m4v files and all 7 had the problem but all were fixed by the simple conversion I performed.

 

The sync issue is bad enough that if it were at all common these boards would be overwhelmed with posts about the problem. Three seconds is a VERY long time in the AV world. Out of sync by as little as 3 or 4 tenths of a second is quite noticeable so ten times that make video impossible to watch.

 

I just wanted to report the problem because it was so bad but you may not need to spend much time on it because it may be quite rare.

 

I also found that on some devices, like my Fire TV, the file direct plays but there is still the aucio ahead of the video by about 3 seconds.

 

All that is why I provided the link to a file that has the problem. I wanted to give the developers, if interested, a file to test with as it is very slow to test by remote control.



#4 Luke OFFLINE  

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Posted 07 April 2020 - 10:40 PM

The stats feature is an option in the video player to see this type of information.



#5 Gilgamesh_48 OFFLINE  

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Posted 08 April 2020 - 12:31 AM

The stats feature is an option in the video player to see this type of information.

The stats feature revealed that I was in error and the file actually is direct playing. In spite of direct plying the audio and video are still way out of sync.

 

I decided to try the remux feature in that menu and when I chose remux the audio and video synced right up. That tells me why passing it through "FFmpeg Batch AV Converter" fixed the problem.

 

I still don't understand why it played perfectly in VLC and was out of sync on "Windows Media Player" and on the Roku when playing through Emby. In the long run it does not really matter as the problem is fixed.



#6 ebr OFFLINE  

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Posted 08 April 2020 - 09:19 AM

I still don't understand why it played perfectly in VLC and was out of sync on "Windows Media Player" 

 

Because VLC could actually be thought of as just a visual interface to ffmpeg.  So, it was probably transcoding it internally.

 

Really sounds like there was something non-standard with the encode (like something that isn't supposed to be in an m4v file) and some players could adjust to it and others couldn't.



#7 Luke OFFLINE  

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Posted 08 April 2020 - 01:40 PM

If it is direct playing then all we can really do is report the issue to Roku along with a sample file.




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