[FFmpeg-user] Windows 10, ffmpeg concat/demux is slow... part 2

Kevin Duffey kevinmduffey at yahoo.com
Sun Nov 12 07:41:43 EET 2017

Hi all,
Posted a thread on this a month or so back, still have not been able to make any headway on why this process is so very slow on my system I am posting again because I am in the process of building a threadripper system mostly for video editing 4K DNxHR and eventually RAW footage, and often I want to combine 2 or more 30 minute to 45 minute long clips into one longer clip before I edit. This is primarily so that I can add a time overlay in the video allowing those viewing it to pick specific bits of the video of interest for various reasons. I post the rendered video to youtube, but I store the original 4K DNxHR SQ/HQ videos for future use to pull the clips from. Thus I want to keep the entire video with the start to end time overlay intact in one video file, so it matches up to whatever someone requests with what they see in the overlay. I also do not want to lose any quality.. e.g. when I do pull clips, I want to pull it from the original high quality 4K source.

With that in mind, I currently have a core i7 6700K, 64GB ram, all NVMe SSD.  In a previous post I was trying to do this via a USB 3 interface, which I thought might have been part of the problem, but turns out even copying the files to my internal SSD first, then concating, still was the same slow speed. 
If other posts I found indicated that this was a normal speed I might accept it... however, I see many posts indicating they get 100, 200 or more fps when concat/demux is being used where I am getting about 5fps to 10fps. After all it isnt decoding/encoding/rendering.. it is just copying two or more files with a bit of update to the file type header to indicate the length change, etc.  Also, I am able to render the same set of clips in Davinci Resolve 14 to mp4 at near real time, about 3x faster than what is going on with the ffmpeg concat process.  
So I feel like I am missing something.  I am doing a very typical concat session. I drop to the CMD, set up a demux.txt file with the two files I want to concat, and then run:
ffmpeg -f concat -safe 0 -i demux.txt -c copy out.mov

Are there any settings, configurations, etc I should be setting up on Windows 10 Home to possibly speed this up?
Does this process typically run faster in linux.. which is my next test.. run this in a vmware linux guest, and see how it performs.
Incidentally, I send this and reply via email.  Is there some way to not top post? A few of you responded last time with telling me not to top post, but I am not sure what that is and how to avoid it when using email replies. 
thank you.

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