Add progress events
Noting here that there should probably be some "progress" events.
Examples
{
// ffmpeg is joining the files (1 hour + 1 hour)
join-progress: 0.52,
// ffmpeg is splitting the joined file to match broadcast (2 hours -> 1.5 hours)
split-progress: 0.81,
// ffmpeg is encoding the final file to MP3 with the correct bitrate
encode-progress: 1.00,
// Knox is uploading to S3
upload-progress: 0.34, // 34%
// Maybe a basic "verb" provided for each stage?
sync-status: 'uploading' // Or: 'encoding' / 'saving' / 'done'
}