w3c validation UTF-8 encoding error

With w3c validator you could get this error:
«Sorry, I am unable to validate this document because on line 3400 it contained one or more bytes that I cannot interpret as utf-8 (in other words, the bytes found are not valid values in the specified Character Encoding). Please check both the content of the file and the character encoding indication.» 
That could be because you have some files included in the php file checked by w3c validator, like an .inc one, not encodeed as UTF-8.
To fix this oproblem you have to encode all the components of a php file as UTF-8.

avidemux too slow

It’s better use (one of) the following codecs for encoding

  • x264
  • libavcodec MPEG-1/MPEG-2
  • libavcodec MPEG-4
  • Xvid 

so Avidemux will be able to optizmize the CPU usage and will be much faster. And the CPU temperature will be lower.
Cfr.here.