DecodeContext constructor tries to free the same context twice when it encounters an error

[SebDaMuffin]

If ffmpeg.avformat_alloc_context() encounters an error, ffmpeg frees the context. The next line then assigns the freed context to _formatContext. Then ffmpeg.avformat_open_input() returns an error, calling Dispose(), which then tries to free the already freed context, resulting in a crash. Delaying the _formatContext assignment until after FFMpegHelper.Verify() fixes this because Dispose() will not try to free _formatContext.

DecodeContext()

MonoGame.Extended2/Sources/MonoGame.Extended.VideoPlayback/DecodeContext.cs

Lines 35 to 37 in a20100b

	var formatContext = ffmpeg.avformat_alloc_context();
	_formatContext = formatContext;
	FFmpegHelper.Verify(ffmpeg.avformat_open_input(&formatContext, url, null, null), Dispose);

Dispose()

MonoGame.Extended2/Sources/MonoGame.Extended.VideoPlayback/DecodeContext.cs

Lines 697 to 701 in a20100b

	if (_formatContext != null)
	{
	ffmpeg.avformat_free_context(_formatContext);
	_formatContext = null;
	}

avformat_alloc_context()

https://github.com/FFmpeg/FFmpeg/blob/00b288da73f45acb78b74bcc40f73c7ba1fff7cb/libavformat/options.c#L187-L192