Aegisub is a free, open-source subtitle editor for Windows and macOS. It creates and modifies timed text for dialogue, on-screen signs and song lyrics, combining an editable subtitle script with audio timing and a video preview. Its Advanced Substation Alpha (ASS) tools control where text appears, how it looks and how it changes during a line.
Aegisub’s subtitle grid and import formats
A subtitle script in Aegisub is a grid of lines with text, start and end times, styles and optional speaker labels. Selecting a line opens its text and controls for editing; selecting several lines allows shared changes. Lines can be split, joined, duplicated or reordered, while comment lines retain notes without appearing over the video. Layers determine which text appears above other text when subtitles overlap.
Aegisub can open ASS, SSA, SRT and MicroDVD subtitles, import dialogue from a plain text script, and read supported subtitle tracks from Matroska video files. Plain text import can separate speaker names from dialogue using a chosen character. Unicode support and selectable legacy character encodings help preserve text in different languages.
Audio timing
Loading an audio file or the soundtrack from a video produces a waveform for matching each subtitle to speech. You set start and end markers, listen to the selected passage and adjust the boundaries. Playback controls also isolate the sound around either boundary, making it possible to check whether the beginning or ending of a word falls outside the line.
The alternative spectrum display represents sound frequencies with color indicating their strength. This gives another view of speech or singing when the waveform is difficult to interpret against background sound. Timing markers can snap to neighboring lines or video keyframes, and keyboard shortcuts support repeated listening and moving through the script.
For changes across multiple lines, Aegisub’s timing post-processor adds lead-in or lead-out time, closes small gaps between adjacent subtitles and adjusts boundaries near keyframes. You control the timing thresholds and can restrict processing to selected lines or styles, leaving separately timed signs and lyrics outside the operation.
Typesetting
ASS styles hold reusable choices for fonts, text colors, outlines, shadows, margins and alignment. Aegisub’s styles manager keeps styles in the current script or in separate storage collections for reuse. Assigning a style applies those choices to a line; override tags change individual properties within the text when a line needs different treatment.
The video preview updates as subtitles are edited. Visual tools let you drag text into position, set movement anchors, rotate it or change its horizontal and vertical scale directly over the image. Rectangular clipping limits the visible text to a box, while vector clipping uses lines and curves to define another shape. These controls are useful for placing a translation over a sign or fitting lettering to an angled surface.
Translation
The Translation Assistant displays the original text beside an entry area for its translation. It advances through text blocks while skipping ASS formatting tags, so the translator can replace the words without retyping the surrounding formatting. Navigation controls return to earlier blocks, and the video can follow the line being translated.
Within the main editor, Show Original retains the line’s original text for comparison. Its Clear Text control removes the words while keeping override tags, which is useful when translating an already positioned sign. Spell checking suggests replacements and accepts additions to the selected dictionary.
Karaoke timing and automation scripts
Aegisub includes a karaoke timing mode for matching parts of lyrics to the soundtrack. Automation extends that work with scripts, including the supplied Karaoke Templater for generating effects from subtitle input. Scripts appear as editing macros, export filters or both, and the Automation Manager controls which scripts are loaded.
Users who write scripts can extend subtitle processing with Lua or MoonScript.
Subtitle export
Export can apply a sequence of filters before producing a subtitle file. Filters can transform timing for a different frame rate, remove redundant formatting tags or limit output to the lines visible at the current video frame. Their order and available settings determine how the script is processed.
ASS retains the positioning and styling used during authoring. Exporting to simpler subtitle formats can remove formatting that those formats cannot represent. Aegisub also collects fonts used by a script so they can accompany the subtitles. Combining the subtitle file with a video container, or rendering it permanently into the picture, uses a separate muxing or encoding program.
