I always used
rtmpdump version 1.x to download videos from 3voor12.vpro.nl, until recently this was no longer possible, so I tried rtmpsuck instead (version 2.3). I should have done that a long time ago, now I only have to give one single command to download a complete video and are no longer troubled by missed key frames.
There was one thing however, a one and a half hour long vid of over 800 MB in size stopped downloading every time I tried after about 70% was downloaded, giving the following error:
"ERROR: Request timeout/select failed, ignoring request
Closing connection... done!"
The only option for rtmpsuck is -z (debug) so I tried that. Downloading (as well as video playback on the website) then became very slow, but after closing the terminal (!) after about 15 (?) minutes, download (as well as playback) continued at normal speed and the video downloaded completely.