Invalid size specified: NaNx480 when using README graphql

[infomofo]

I have tried integrating this plugin with my blog and I'm getting the following error.

 ERROR
Invalid size specified: NaNx480

  Error: Invalid size specified: NaNx480
  - videosize.js:145 createSizeFilters
    [myblog]/[fluent-ffmpeg]/lib/options/videosize.js:145:11
  - videosize.js:209 FfmpegCommand.proto.withSize.proto.setSize.proto.size
    [myblog]/[fluent-ffmpeg]/lib/options/videosize.js:209:19
  - index.js:112
    [myblog]/[gatsby-plugin-ffmpeg]/lib/index.js:112:37
  - Array.forEach
  - index.js:88 processFile
    [myblog]/[gatsby-plugin-ffmpeg]/lib/index.js:88:8
  - task_queues.js:97 processTicksAndRejections
    internal/process/task_queues.js:97:5

My markdown has a frontmatter field like:

      video: ./side-two.mp4

And in my graphql for the node I query it as:

        frontmatter {
              video {
                childVideoFfmpeg {
                  mp4: transcode(maxWidth: 900, maxHeight: 480, fileExtension: "mp4", codec: "libx264", options: [["-profile:v", "main"], ["-pix_fmt", "yuv420p"]], outputOptions: ["-movflags faststart"]) {
                    width
                    src
                    presentationMaxWidth
                    presentationMaxHeight
                    originalName
                    height
                    aspectRatio
                  }
                }
              }
            }
}

Which is the sample graphql code from the README.

I'm on a mac and using ffmpeg using the install instructions from your other readme here.

I'm running in gatsby develop and whenever I hit this error, either in a post query, or in the graphql editor, the process exits. Even running in verbose mode I don't get any further explanation than the error above.

Any ideas what I'm doing wrong?