gist.cs

public async Task<Stream> CompressVideo(MediaFile file)
{

	string exportPath = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
	string exportFilePath = Path.Combine(exportPath, "compressed_video.mp4");

	System.Diagnostics.Debug.WriteLine("Export path: " +  exportPath);
	System.Diagnostics.Debug.WriteLine("Export file path: " + exportFilePath);

	var asset = AVAsset.FromUrl(NSUrl.FromFilename(file.Path));
	AVAssetExportSession export = new AVAssetExportSession(asset, AVAssetExportSessionPreset.MediumQuality);

	System.Diagnostics.Debug.WriteLine("Created export object");

	export.OutputUrl = NSUrl.FromFilename(exportFilePath);
	export.OutputFileType = AVFileType.Mpeg4;
	export.ShouldOptimizeForNetworkUse = true;

	System.Diagnostics.Debug.WriteLine("Preparing to export");

	await runExportAsync(export);

	Stream exportStream = File.OpenRead(exportFilePath);

	System.Diagnostics.Debug.WriteLine("Stream read from file");

	return exportStream;
}

private async Task RunExportAsync(AVAssetExportSession exp)
{
	await exp.ExportTaskAsync();
	if (exp.Status == AVAssetExportSessionStatus.Completed)
	{
		System.Diagnostics.Debug.WriteLine("Finished export");
	}
}