Support for avformat_open_input options

[ccaum]

Previous to this commit, no options could be given to the FmtCtx.OpenInput function. For input formats like video4linux2, that means options to specify input format (rawvideo, h264, etc.) or framerate were impossible.

This commit introduces a new FmtCtx.OpenInputWithOption function that takes a Option parameter. To maintain backwards compatibility, the OpenInput function now just calls the OpenInputWithOption function, but passes a nil value for the Option parameter.

Example usage:

  inputOptionsDict := gmf.NewDict([]gmf.Pair{
          {"white_balance_auto_preset","4"},
          {"input_format", "h264"},
  })

  inputCtx := gmf.NewCtx()
  inputCtx.SetInputFormat("video4linux2")

  inputOption := &gmf.Option{Key: "video4linux_input_options", Val: inputOptionsDict}

  err := inputCtx.OpenInputWithOption("/dev/video0", inputOption)

[3d0c]

Hi, @ccaum. Yes, looks good, but i found two problems:

• please change cfilename type from *_Ctype_char
• please check that examples work, i tried video-to-image and it fails with SIGSEGV

  github.com/3d0c/gmf.(*FmtCtx).OpenInputWithOption(0xc00009c270, 0x7fff5fbff9ee, 0x7, 0x0, 0x0, 0x0)
  /Users/alex/3d0c/gmf/format_go112.go:222 +0x6b

[ccaum]

Sorry for the delay. Thanks for catching those issues. All fixed.

[3d0c]

I added small fix for format_go112.go. Now everything looks good. Thank you.