Add option to configure b-frames `-bf`

[Euklios]

Is your feature request related to a problem? Please describe.
Sources from the issue #318.
FFmpeg tends to emits b-frames, which are not understood by all parsers.

Describe the solution you'd like
There should be an option to configure bframes, which should allow to disable them entirely -bf 0.

Describe alternatives you've considered
This could also be done using extraArgs

[Euklios]

@AlexanderSchuetz97 for documentation purposes:
To my understanding, the option -bf specifies how many b-frames ffmpeg is allowed to emit between I/P-Frames.
So -bf 2 allows 2 b frames, while -bf 0 essentially limits the number of b-frames to 0, therefore disabling it.

[AlexanderSchuetz97]

Your understanding matches mine.
I have to deal with decoders for h264 for example that cannot handle bframes so I have to turn them off. If one of those decoders attempts to decode a video stream with b frames then the video will jitter as it will play the frames in the order that it has read them. This means that the video will appear to playback in reverse sometimes for half a second before jumping forward a second again.

I do not think I will ever set a value other than 0 explicitly, but that is my, someone else may need to set this to 1 or higher forwhatever reason. I have observed that 2 appears to be the default that ffmpeg uses if you specify nothing. (I have seen this in ffprobes output from looking at created files)