This is an error raised by ffmpeg, however I've no idea why. It works for me, I can even download from the URL provided in the first post.
If you run SVP 4\utils\ffmpeg.exe what you should see is:
C:\Program Files (x86)\SVP 4\utils>ffmpeg
ffmpeg version 3.2.2 Copyright (c) 2000-2016 the FFmpeg developers
...
The next step is to download via ffmpeg manually:
- choose the video, click on "Copy URL" in SVPtube
- in the console window type
ffmpeg -y -i "PASTE-URL-HERE" -vcodec copy LOCAL-PATH
Example:
ffmpeg -y -i "https://r7---sn-v2u0n-hxal.googlevideo.com/videoplayback?id=1e7f64ba68db2644&itag=315&source=youtube&requiressl=yes&mm=31&mv=m&ms=au&mn=sn-v2u0n-hxal&pl=18&initcwndbps=1525000&ratebypass=yes&mime=video/webm&gir=yes&clen=1682579394&lmt=1481457970074412&dur=516.366&upn=EFi5PZsloCU&mt=1485487224&signature=9AE6BF901DC29DBE7D39C77527B7DFA6286A5528.1A6FADC44837C85E4A2A5A3FFD98402225835DF8&key=dg_yt0&ip=122.105.196.234&ipbits=0&expire=1485509088&sparams=ip,ipbits,expire,id,itag,source,requiressl,mm,mv,ms,mn,pl,initcwndbps,ratebypass,mime,gir,clen,lmt,dur" -vcodec copy d:\test.webm