.avi working / anything else not working

FFMPEG ERROR: Execute error. Output for file "/***/***/***/public_html/files/tmp/1211632903501.mpg" was not found. Please check server write permissions and/or available codecs compiled with FFmpeg. You can check the encode decode availability by inspecting the output array from PHPVideoToolkit::getFFmpegInfo().

i've tried printing the output array as stated above, but its mostly empty:
Array
(
[compiler] => Array
(
[configuration] => Array
(
)

[vhook-support] =>
[versions] => Array
(
)

)

[formats] => Array
(
)

[filters] => Array
(
)

[protocols] => Array
(
)

[abbreviations] => Array
(
)

[ffmpeg-php-support] => module
)

also; i get this error:
Use of undefined constant OS_WINDOWS - assumed 'OS_WINDOWS'

to summarize: .avi converts to .flv just fine. anything else doesn't, and creates the above errors...

i have ffmpeg / flvtools2 installed, aswell as "Ruby" or smth like that to make sure flvtools2 worked ( according to my host )

any help will be greatly appriciated :)

UPDATE:

thanks to my host, i changed line 205:
const FORMAT_MP3 = 'mp3';
to
const FORMAT_MP3 = 'libmp3lame';

and it all started working with .mpg, .wmv aswell as .avi.
have not tried more formats yet, but will do so...

I'm still hoping for some input as to why this had to be changed, and
as to why the OS_WINDOWS is not defined, and what should I put in it...
const OS_WINDOWS = '???';

btw, my server has linux... ( dont know if that has anything to do with it )