Video formats, captions and metrics

Aspect ratios, resolution, frame rate, codecs, captions, voiceover and retention metrics. 21 terms, each with what it means, why it matters and what to do about it.

Animated captions

Animated captions are on-screen captions that appear or highlight word by word in time with speech, common in Reels, TikTok and Shorts.

Aspect ratio

Aspect ratio is the shape of an image or video, written as width to height, such as 16:9 for widescreen or 9:16 for vertical video.

Audience retention

Audience retention shows what share of viewers are still watching at each moment of a video, revealing where people drop off.

Average view duration (AVD)

Average view duration (AVD) is the average time viewers watch a video, found by dividing total watch time by the number of views.

Bitrate

Bitrate is how much data a video or audio file uses per second, usually in Mbps or kbps. Higher bitrate usually means better quality and bigger files.

Closed captions (CC)

Closed captions (CC) are text versions of a video's speech and key sounds that viewers can turn on or off, made for deaf and hard-of-hearing viewers.

Codec

A codec is software that compresses and decompresses video or audio. H.264 is the most widely supported; H.265 (HEVC) and AV1 are newer and more efficient.

Completion rate

Completion rate is the percentage of video views that reach the end. In ads it is often called view-through rate (VTR).

Frame rate (FPS)

Frame rate is how many still images a video shows each second, measured in frames per second (FPS). Common rates are 24, 30 and 60 FPS.

Lip sync

Lip sync is matching mouth movements to audio, whether a person mouthing words to a song or AI that animates a face to match a voice track.

MP4

MP4 is the most common video file format: a container that holds video, audio and subtitles, accepted by almost every platform, browser and phone.

Open captions

Open captions are captions burned into the video picture, so they always show and cannot be turned off. They are the norm for social video.

Royalty-free music

Royalty-free music is music licensed for a one-time fee or subscription, with no per-play royalties, so you can use it in videos and ads.

Safe zone

A safe zone is the area of a video or image where text and key content will not be hidden by platform buttons, captions or cropping.

SRT file

An SRT file is a plain-text subtitle file listing numbered captions with start and end times. Most video platforms and players accept it.

Subtitles

Subtitles are on-screen text of the spoken words in a video, often translated, for viewers who can hear the audio but need or prefer to read it.

Text to speech (TTS)

Text to speech (TTS) is technology that turns written text into spoken audio, used for voiceovers, accessibility and voice assistants.

Video resolution

Video resolution is the number of pixels in each frame, written as width x height or a shorthand like 1080p or 4K. More pixels means more detail.

Video thumbnail

A video thumbnail is the still image shown before a video plays. It works like a cover and strongly affects whether people click or tap.

Voiceover

A voiceover is narration recorded separately from the picture and laid over a video to explain, tell a story or guide the viewer.

Watch time

Watch time is the total time people spent watching your video or channel. Platforms like YouTube use it as a key signal of quality.