Ok, so threads => 0 works good with mp4, but with webm the "0" doesn't work, so I changed it to threads => 7. I added cpu_used => 5 to the code for webm and it slightly speeds it up, but I am unable to add token-parts => 3, and 'deadline realtime'. Threads won't work correctly for webm without token-parts and I think that 'deadline realtime' is looking for a number after it but a numerical value can't be set for it. That is the real reason why I don't want to use webm, because it takes forever to transcode.

source: webmproject (dot) org/docs/encoder-parameters/

Here's what's happening to me: 'token-parts' causes webm to fail and 'deadline realtime' causes webm to fail too, even after trying them all separately.

Here is my unserialized code:

array (

  'h' => '480',

  'force_type' => 'webm',

  'ffmpeg_options' => 

  array (

    'threads' => 7,

    'cpu-used' => 5,

    'token-parts' => 3,

    'deadline realtime',

  ),

);;