FFmpegIO automatic format parsing

[stashymane]

With FFmpegIO input/output streams, you currently have to specify the format manually, however in my use-case it's not always possible to pre-determine the format with either the file name or user input - the only option is to open the file and attempt to read. Would be great if FFmpegIO could automatically determine the file format (with FFProbe, for example).

[Manevolent]

I think there is an option for us to be able to do this. I will keep this in mind; it may require seeking, but I just added that with SeekableByteChannels.