Allow Initial Parameters

[syntaxevolution]

Is your feature request related to a problem? Please describe.
php-ffmpeg allows you to set initial parameters now and the latest prerelease is using this version of php-ffmpeg but doesn't allow setting of the initial parameters.

Describe the solution you'd like
Ability to call setInitialParameters just as in php-ffmpeg

Describe alternatives you've considered
No other method of setting initial parameters such as -presets veryfast at the moment.

Additional context
Please see PHP-FFMpeg/PHP-FFMpeg#703

[aminyazdanpanah]

Usage:

$format = new X264();
$format->setInitialParameters(['param1', 'param2', ...]);

$ffmpeg = Streaming\FFMpeg::create();

$video = $ffmpeg->open('/var/media/video.mp4');

$video->hls()
    ->setFormat($format)
    ->autoGenerateRepresentations([720, 480])
    ->save('/var/media/hls.m3u8');