Error rendering on ec2 : Specified pix_fmt is not supported Here is the context, i have a amazon ec2 micro instance with ubuntu 14.04 and with blender 2.78 installed, i have a custom blend file with in output : file_format is H.264, color_mode is RGBA, in Encoding format is AVI and Codec is PNG. The problem is that when i launch rendering by the command line, the render fails and in the log i get this message : 

Error: Specified pix_fmt is not supported

It may be a ffmpeg problem which i installed prior to blender following this :
http://www.faqforge.com/linux/how-to-install-ffmpeg-on-ubuntu-14-04/

When i render it locally (Ubuntu 16.04, ffmpeg, blender 2.78) it works just fine.

Has anyone any idea how to resolve this?

Thanx.
Chances are your remote FFMPEG is missing one of the legion of codecs when it was compiled. You will need to use a version compiled with the codec required.