Closed Caption and Subtitle Frame Rates for the Digital Distribution of TV and Film
In April, we held a webinar with Netflix and the Entertainment Merchants Association on the best practices for closed captioning the digital distribution of TV and film. Sean Bersell, the VP of Public Affairs at the Entertainment Merchants Association, discussed (among other things) the best practices for caption frame rates and how to convey information about the frame rate for caption files. These best practices were proposed by the EMA Closed Captions Working Group, consisting of Amazon, Best Buy, Google, Microsoft, MovieLabs, Netflix, Rovi, Vudu, and the EMA. The group was created to develop closed captioning best practices for compliance with federal legal requirements.
The Issue with Frame Rates for Online Video
The main issue is that ideally, the caption (or subtitle) frame rate should match the native frame rate of the source video. However, oftentimes this is not the case, and the synchronization of the two can be a problem. The main problem here is that the frame rate requirements for broadcast TV do not match the frame rate requirements for Internet video. The frame rate of the caption file must be reconfigured when the video is transitioned from television to the Internet. Some video distributors require that the captions and video be synched when the file is delivered to them; others will take unsynched caption files.
Best Practices for Closed Caption and Subtitle Frame Rates
For those distributors who will take unsynched caption (or subtitle) files, the best practices are for the closed caption file to be submitted in any frame rate in which it was created, so long as the frame rate is clearly indicated. For SCC files, the file name should indicate whether the file is drop-frame (DF) or non-drop-frame (NDF), as the protocol for the time code depends upon this differentiation. DF files use a semicolon between seconds and frames (hours:minutes:seconds;frames) while NDF files use all colons (hours:minutes:seconds:frames).
How to Convert Caption or Subtitle Frame Rate
If the video distributors require the file to be synched when delivered, you must convert your caption or subtitle frame rate so it is synchronized with the video ahead of time.
We encourage you to read the white paper to learn further best practices, standards, and legal requirements for closed captioning.