OT: A few ffmpeg queries

[Vangelis forthnet]

> ffmpeg -i progname.ts -c:av copy progname.mp4

Very early in the morning here, so I'll be laconic for now :-)
Assuming you've not mistyped it, 

-c:av copy 

is not valid and probably the reason your command 
is initiating video+audio transcoding... Try 

ffmpeg -i progname.ts -c copy progname.mp4 

and see how that fares... 

-c copy = 
-vcodec copy -acodec copy 
or 
-c:v copy -c:a copy
or 
-codec: copy
or 
-codec copy

https://ffmpeg.org/ffmpeg.html#toc-Stream-copy
https://ffmpeg.org/ffmpeg.html#toc-Stream-specifiers-1

According to 
https://en.wikipedia.org/wiki/Comparison_of_video_container_formats
the MP4 container should be able to support both 
https://en.wikipedia.org/wiki/H.262/MPEG-2_Part_2 (video) 
and 
https://en.wikipedia.org/wiki/MPEG-1_Audio_Layer_II (audio) 
raw streams, playing back such a file in a HW/SW player 
is another matter, though (most expect h264+aac). 
The question is, why must you use the MP4 container in your NAS? 

V.