Subtitle glossary

ASS

Advanced SubStation Alpha. A rich subtitle format with styling, positioning and animation. See ASS reference.

Burn-in

Baking subtitles into the video frames so they cannot be turned off. Also called hardcoded or open captions.

Caption

A subtitle track for deaf and hard-of-hearing viewers that includes sound effects and speaker labels in addition to dialogue. Also see SDH.

Closed caption (CC)

A caption track that viewers can turn on or off. Delivered as a separate stream or file.

CPS

Characters per second. A measure of reading speed. Common subtitle targets are 15–17 CPS for general content, 12 CPS for children, 17–20 CPS for SDH.

Cue

A single subtitle unit: start time, end time and dialogue text. Files are made up of multiple cues.

Cue identifier

An optional label before a cue timestamp in WebVTT. Used for targeting cues with CSS or JavaScript. SRT uses numeric cue numbers instead.

Forced narrative

A subtitle that translates on-screen foreign-language dialogue or text that is essential to the plot. Usually displayed on top of the primary subtitle track.

Frame rate

The number of video frames per second. Common values: 23.976, 24, 25, 29.97. Frame rate affects timing in frame-based subtitle formats (e.g. SUB / MicroDVD).

Hardsub

Subtitles burned into the video. Same as burn-in.

Lead-in

The small amount of time a subtitle appears before the corresponding dialogue starts. Typically 100–200ms.

Lead-out

The small amount of time a subtitle remains after the corresponding dialogue ends. Typically 100–300ms.

MicroDVD

A frame-based subtitle format using the .sub extension. See SUB reference.

Open caption

A caption track that is always visible (not selectable). Usually burned into the video.

Reading speed

How fast a viewer can read subtitles. Measured in CPS or WPM. See the reading speed guide.

SDH

Subtitles for the Deaf and Hard-of-Hearing. Includes dialogue plus descriptions of non-dialogue audio (sound effects, music cues, speaker identification).

Soft subtitle

A subtitle delivered as a separate stream or file that viewers can turn on or off. The opposite of burn-in.

Spotting

The process of marking when each line of dialogue begins and ends in the timeline. Produces the timings that go into the subtitle file.

SRT

SubRip subtitle format. The most widely supported subtitle format. See SRT reference.

SSA

SubStation Alpha. Predecessor to ASS. See SSA reference.

Timestamp

The start or end time of a cue. Formats differ in timestamp syntax (SRT uses commas, WebVTT uses periods).

VTT

WebVTT. The W3C standard subtitle format for HTML5 video. See WebVTT reference.

WPM

Words per minute. A reading-speed measure that is sometimes used alongside CPS. For subtitles, CPS is more common because it accounts for character density.