Subtitle Glossary

Plain definitions of the terms used in subtitling, from file formats like SRT to quality measures like reading speed (CPS). Each entry links to a fuller explanation where one exists.

ASS (Advanced SubStation Alpha): A subtitle format that supports detailed styling, positioning, fonts, and effects. Common in fansubbing and karaoke captions, where appearance matters more than portability. Read more →
Auto-captions: Captions generated automatically from a transcript, without the formatting that makes subtitles readable. Often accurate word for word but tiring to follow because reading speed, line breaks, and timing are not applied. Read more →
Burned-in subtitles (hardcoded): Subtitles rendered permanently into the video image. They are always visible, travel with the file everywhere, and cannot be turned off by the viewer. Read more →
Captions: Text built for accessibility that presents spoken dialogue plus relevant non-speech audio, such as music, sound effects, and speaker labels, usually in the same language as the audio. Read more →
Closed captions: A separate caption track the viewer can turn on or off in the player. Often delivered as an SRT or other timed-text file. Read more →
CPL (characters per line): The number of characters on a single subtitle line, including spaces and punctuation. A widely used limit is 42 CPL, with up to two lines per subtitle. Read more →
CPS (characters per second): The unit used to measure subtitle reading speed: the number of characters shown per second of display time. 17 CPS is the standard for general audiences. Read more →
Cue (subtitle block): A single subtitle entry: a sequence number, a start and end timecode, and the text shown during that interval. Read more →
Forced subtitles (forced narrative): Subtitles shown only for parts the audience needs translated even when watching in the original language, such as on-screen text or a line of foreign dialogue.
Frame rate: The number of video frames shown per second, such as 24 or 25 fps. Subtitle timecodes are frame-accurate, so a mismatch in frame rate between the subtitle file and the video can shift the timing.
Open captions: Captions that are always visible and cannot be turned off. In practice this is often achieved by burning the subtitles into the video. Read more →
Reading speed: How fast subtitle text appears relative to the time it is on screen, measured in characters per second (CPS). One of the most important subtitle quality factors. Read more →
SDH (Subtitles for the Deaf and Hard of Hearing): Subtitles that combine the readability of professional subtitling with accessibility information such as speaker labels, music cues, and sound effects. Read more →
Segmentation: Where subtitle text is broken across lines and cards. Professional subtitles break at phrase boundaries, not mid-phrase, so each line reads as a complete thought. Read more →
Soft subtitles (subtitle track): Subtitles kept as a separate track from the video image, which the viewer can toggle on or off. The opposite of burned-in subtitles. Read more →
Spotting (cueing): Setting the in and out times for each subtitle: the exact timestamps when a subtitle appears and disappears. Read more →
SRT (SubRip Subtitle): The most widely supported subtitle file format. A plain text file of numbered cues, each with a start and end timecode and the subtitle text. Read more →
Subtitles: Spoken dialogue presented as readable on-screen text, often translated, shaped for reading with controlled reading speed, line breaks, and timing. Read more →
Sync (synchronization): The alignment of subtitles with the audio. When every subtitle is off by the same fixed amount, a single timing shift brings them back into sync. Read more →
Timecode: The time reference, in hours, minutes, seconds, and frames or milliseconds, that marks when a subtitle appears and disappears. Read more →
Timing: When a subtitle appears, how long it stays, and when it leaves. Good timing follows spoken rhythm and holds each subtitle long enough to read. Read more →
Transcription: Turning speech into text. A necessary first step, but not the same as subtitling, which shapes that text into readable, well-timed subtitles. Read more →
WebVTT (VTT): A subtitle format built for web and HTML5 video. Similar to SRT but with a WEBVTT header and support for positioning and styling cues. Read more →