This most recent zencoder-php SDK throws the following exception as a result of any API requests:
Response header is missing Content-Type

The reason appears to be that the SDK checks for the following response header: Content-Type. A recent change to Zencoder appears to have resulted in all response headers being returned in lower case. So the SDK is not finding the new content-type lower case header and throwing the above exception.

A quick and dirty fix we applied was to use the following code in the Services/Zencoder.php _processResponse($response) function (line 234):

if (empty($headers['Content-Type'])) {
    if (empty($headers['content-type'])) {
        throw new Services_Zencoder_Exception('Response header is missing Content-Type', $body);
    } else {
        $headers['Content-Type'] = $headers['content-type'];
    }
}