“The video you have sent me does not work.”

• Matroska file format is not supported.
• H.264 video is supported, but not with the default yuvj422p color format.
• MP3 sound is supported, but the sample rate 22050 S/s (and probably others) is not supported.

Suggested solutions:

• Convince your client to use a better operating system.
• Convince your client to install video player with non-Microsoft codecs.
• Quit "computers" job.
• Use the following avconv command line.

avconv -i infile -ar 48000 -acodec libmp3lame -pix_fmt yuv420p -y outfile.mp4