Create ability to define additional filters per stream in the HLSPlaylistExporter

[chancezeus]

As specified in title/commit message I needed the ability to add filters per format (scale/framerate).

For this purpose I added the option to add (multiple) filters to the addFormat function (these per stream filters work exactly the same as the addFilter method on the media object).

As more people might be interested I submit this pull request for you to review and/or merge (if wanted/needed).

[pascalbaljet]

Thanks for the PR! I like the feature but this would be a breaking change. I'll try to find some time to refactor this into a non-breaking change and then add it as a feature.

[pascalbaljet]

As of version 1.2.0 the addFormat method of the HLS exporter takes an optional second parameter which can be a callback method. This allows you to add different filters per format:

$lowBitrate = (new X264)->setKiloBitrate(250);
$highBitrate = (new X264)->setKiloBitrate(1000);

FFMpeg::open('steve_howe.mp4')
    ->exportForHLS()
    ->addFormat($lowBitrate, function($media) {
        $media->addFilter(function ($filters) {
            $filters->resize(new \FFMpeg\Coordinate\Dimension(640, 480));
        });
    })
    ->addFormat($highBitrate, function($media) {
        $media->addFilter(function ($filters) {
            $filters->resize(new \FFMpeg\Coordinate\Dimension(1280, 960));
        });
    })
    ->save('adaptive_steve.m3u8');