Add an option to show video output on a drawable without video effects

[levs42]

Description & motivation

This PR brings an option to display camera output on a drawable before applying the video effects. It allows to show the video effects only on the stream. Default value is the same as before. effectsBuffer flags helps to prevent the race condition when the video effects appear on the drawable for some frames; it happens when effects rendering is faster than drawable rendering.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

[shogo4405]

With HKView.isCaptureVideoPreviewEnabled = true, it's possible to preview the unprocessed video. Could this feature serve as an alternative?

[levs42]

I tried isCaptureVideoPreviewEnabled but it doesn't lead to the same result. Here is what I'm trying to achieve with the PR:

Screenshots

The preview shows two effects. First is time effect. Second is "view effect" of two yellow bars, a UIView is getting displayed on the screen and is getting rendered as a visual effect. The video preview displays both effects. The preview is in resizeAspectFill mode. This is the current behavior.

When HKView.drawWithEffects = false and Stream.videoMixerSettings.effectsBuffer = true both effects are not present on the preview:

[levs42]

I found the cause. Looks like HKView.isCaptureVideoPreviewEnabled = true works only for macos because it always creates an extra buffer. I'm going to keep effectsBuffer flag for other platforms to be able to achieve the same behavior.

[shogo4405]

I see, understood. I accept changes of this magnitude. I'd like the variable name to be changed to "isXXXXEnabled". For example, "isEffectsBufferEnabled" is a bit unclear to me. Do you have any other suggestions for a more appropriate name?

[levs42]

We could use "alwaysUseBufferPoolForVideoEffects" or similar. "always" might be a good choice because even when the flag is false, macos will use the buffer pool. And when the flag is true, pixel buffer pool will always be used. Alternatively, we could add a new enum to the settings:

enum EffectsRenderMode {
   /// This mode tries to save memory on non-macos platforms by rendering to the video output pixel buffer.
   case optimized
   /// This mode is always using a separate pixel buffer to render the video effects.
   case separateBuffer
}

[shogo4405]

Let's go with "alwaysUseBufferPoolForVideoEffects".

[levs42]

Updated, please take a look

[shogo4405]

👍 Thank you.