go-timecode is a Go library for SMPTE ST 12-1-2014 timecodes.

• correct drop-frame and non-drop-frame support
• all standard film, video and TV edit rates 23.976, 24, 25, 29.97, 30, 48, 50, 59.94, 60, 96, 100, 120
• arbitrary user-defined edit rates down to 1ns precision with a timecode runtime of ~9 years
• conversion between timecode, frame number and realtime
• timecode and frame calculations
• timecode & rate fit into a single 64bit integer for efficient binary storage
• parses and outputs SMPTE ST 12-1 timecode with DF flag
• different output methods to include and parse edit rate with timecode strings

Many timecode libraries treat timecode values as literal wall-clock time which they are not. Instead, timecodes are mere address labels for edit units in a sequence of video frames or audio samples. With a different edit rate, the same frame in a sequence has a different timecode address.

It's probably the reason why drop-frame timecodes are often misunderstood. I guess it's better to call them skip-timecodes because that's what's happening. At 29.97fps each edit unit has a duration of 33.3666ms, 30 such edit units last for 1.001s. Hence, a 29.97DF timecode of 00:00:01;00 actually means 1.001s instead of 1s. Now this makes it obvious that the time-part of the timecode runs a bit slower than realtime. To compensate for this speed issue, a drop-frame timecode skips some address labels now and then. To be precise, it skips frame labels ??:??:??;00 and ??:??:??;01 every minute but not every 10th minute. That's all.

• API Reference
• FAQ

Install go-timecode using the "go get" command:

go get github.com/trimmer-io/go-timecode/timecode

The Go distribution is go-timecode's only dependency.

import "github.com/trimmer-io/go-timecode/timecode"

tc := timecode.Parse("00:00:59;29")
tc.SetRate(timecode.Rate30DF)
tc.Add(2*time.Minute)
fmt.Println("Frame number at TC", tc, "is", tc.Frame())

See CONTRIBUTING.md.

go-timecode is available under the Apache License, Version 2.0.