iOS/Android Video Decoding

[swoolcock]

VideoDecoder does not currently work on iOS nor Android, as we do not include compatible native libraries for ffmpeg.

We have a couple of options:

1. Attempt to get MobileFFmpeg static libraries working with the FFmpeg.AutoGen package. https://github.com/tanersener/mobile-ffmpeg

2. Abstract VideoDecoder to not be implementation-specific, then subclass it per platform.
   Android could use Xamarin.Android.MP4Transcoder, which is based on ffmpeg.
   iOS would likely need to use AVFoundation, as I could not find an ffmpeg-based wrapper.
   Desktop would continue to use FFmpeg.AutoGen.

Edit: It looks like there are potentially licensing issues with using ffmpeg under Android. The previously mentioned MP4Transcoder is actually based on this custom transcoder: https://github.com/ypresto/android-transcoder

[peppy]

I think we'll probably want #2 for performance reasons.

[UselessToucan]

Not sure that it can be used in our case, but VideoLAN recently released .NET bindings for LibVLC(with Xamarin.Android and Xamarin.iOS support)
You can find the library here https://code.videolan.org/videolan/LibVLCSharp

[swoolcock]

@UselessToucan Yeah I might take a look at that, I don't think AVFoundation is going to do what we need it to do. It's tricky to process raw data in realtime, unless we fully read the stream first. That's not really an option if you want to play large video files.

[swoolcock]

Looking deeper into this, I feel that LibVLC may not be a good solution for us. Calling Stop() on the player is a blocking action, since it waits for all the active LibVLC threads to join. It's incredibly fiddly to make sure all LibVLC threads have exited, otherwise it's likely to freeze and/or crash the app. I would rather find a native solution that is proven for the platform.

I think I've worked out a way of asynchronously reading/playing an AVAsset from a System.IO.Stream, so that should cover iOS. I'll look at Xamarin.Android.MP4Transcoder when I get a chance, but I'm guessing it will be a lot easier to implement than iOS.