My setup:
Zoneminder v1.28.1
Ubuntu 14.04 Server

– First I open the event by clicking on the event number and the video starts to play
– Then I click the ‘Video’ link just above the video playing (this gives me the video popup)
– I accept the defaults and click the ‘Generate Video’ button
– Then I get the ‘Video Generation Failed!’ message

The System Log entry from Zoneminder Console:
“Unable to generate video, check /usr/share/zoneminder/events/2/15/04/16/10/51/59/ffmpeg.log for details”

– I don’t find an ffmpeg.log there, only the individual image files and the zmEventDetail.html and zmEventImages.html files

In the /var/log/apache2/error.log, I see these corresponding entries to my failed video export attempt:

Source: Video Generation Failed – ZoneMinder Forums