Language reference

vedit programmes are postfix: literals and sources push values, while operations consume values from the top of the stack and push results. Signatures below show the stack from left to right, with the rightmost value at the top. For example, VIDEO DURATION -> VIDEO means that the duration is popped first, followed by the video.

Comments begin with # outside a quoted path. Each source, literal, or operation occupies one line.

Value types

Type	Meaning
VIDEO	A video stream that can be edited independently.
AUDIO	An audio stream that can be edited independently.
COMBINED	Ordered media tracks and attachments, plus chapters and container tags.
SUBTITLES	A text, ASS/SSA, or bitmap subtitle track; its concrete kind is probed.
BURN_STYLE	Validated appearance settings used when rendering subtitles into video.
INDEX	A non-negative integer used to address tracks in a combined value.
DURATION	A non-negative time value in seconds internally.
SCALAR	A finite floating-point number used for volume and speed.
BOOL	A compile-time Boolean used by logic and structured control flow.
STRING	A quoted metadata key, value, title, or language.
CHAPTER	A chapter interval and title waiting to be added.
ATTACHMENT	An external attachment waiting to be added.

Sources and literals

Form	Signature	Description
video "path"	() -> VIDEO	Push the first video stream from an input.
audio "path"	() -> AUDIO	Push the first audio stream from an input.
combined "path"	() -> COMBINED	Push every video, audio, and subtitle stream from one input.
subtitles "path"	() -> SUBTITLES	Push a subtitle input.
duration 5s	() -> DURATION	Push seconds. Decimals are accepted.
duration 250ms	() -> DURATION	Push milliseconds.
duration 01:23.500	() -> DURATION	Push a minutes:seconds duration.
scalar 0.7	() -> SCALAR	Push a finite floating-point value.
index 0	() -> INDEX	Push a zero-based track index.
burn-style "size=42; color=#FFFFFF"	() -> BURN_STYLE	Push validated burn settings.
string "Japanese"	() -> STRING	Push a metadata string.
attachment "font.ttf"	() -> ATTACHMENT	Push an external attachment; common font and image MIME types are inferred.
true	() -> BOOL	Push true.
false	() -> BOOL	Push false.

Paths must be quoted and may contain spaces or # characters.

Quoted strings support positional interpolation: video "$1" substitutes the first script argument, while video "clips/$2.mp4" inserts the second argument into a larger string. $0 and references to missing arguments are rejected. Source paths must remain quoted.

Stack operations

Operation	Signature	Effect
dup	A -> A A	Duplicate the top value.
drop	A -> ()	Discard the top value.
swap	A B -> B A	Exchange the top two values.
over	A B -> A B A	Copy the second value to the top.
rot	A B C -> B C A	Rotate the third value to the top.

A, B, and C may be values of any type. Duplicated media is automatically routed through an FFmpeg split or asplit only when multiple reachable consumers require it.

Combined media

Operation	Signature	Description
get-video	COMBINED -> VIDEO	Extract the first video track.
get-audio	COMBINED -> AUDIO	Extract the first audio track.
get-subtitles	COMBINED -> SUBTITLES	Extract the first subtitle track.
split	COMBINED -> VIDEO AUDIO	Extract the first video and audio tracks, with audio on top.
mux	VIDEO AUDIO -> COMBINED	Combine independently edited video and audio. Ordering is strict.
attach-subtitles	COMBINED SUBTITLES -> COMBINED	Append subtitles; alias of add-subtitles.
video-to-combined	VIDEO -> COMBINED	Wrap a video with empty audio and subtitle collections.

The compatibility extractors select track zero and discard the remaining combined value. Indexed operations preserve or modify the collection:

Operation	Signature	Description
video-at	COMBINED INDEX -> COMBINED VIDEO	Copy an indexed video track.
audio-at	COMBINED INDEX -> COMBINED AUDIO	Copy an indexed audio track.
subtitles-at	COMBINED INDEX -> COMBINED SUBTITLES	Copy an indexed subtitle track.
take-video	COMBINED INDEX -> COMBINED VIDEO	Remove and return an indexed video track.
take-audio	COMBINED INDEX -> COMBINED AUDIO	Remove and return an indexed audio track.
take-subtitles	COMBINED INDEX -> COMBINED SUBTITLES	Remove and return an indexed subtitle track.
drop-video	COMBINED INDEX -> COMBINED	Remove an indexed video track.
drop-audio	COMBINED INDEX -> COMBINED	Remove an indexed audio track.
drop-subtitles	COMBINED INDEX -> COMBINED	Remove an indexed subtitle track.
add-video	COMBINED VIDEO -> COMBINED	Append a video track.
add-audio	COMBINED AUDIO -> COMBINED	Append an audio track.
add-subtitles	COMBINED SUBTITLES -> COMBINED	Append a subtitle track.
replace-video	COMBINED INDEX VIDEO -> COMBINED	Replace an indexed video track.
replace-audio	COMBINED INDEX AUDIO -> COMBINED	Replace an indexed audio track.
replace-subtitles	COMBINED INDEX SUBTITLES -> COMBINED	Replace an indexed subtitle track.
move-video	COMBINED FROM TO -> COMBINED	Reposition a video track.
move-audio	COMBINED FROM TO -> COMBINED	Reposition an audio track.
move-subtitles	COMBINED FROM TO -> COMBINED	Reposition a subtitle track.

Indexes are zero-based. Invalid indexes fail during compilation. Per-type collection order determines the final mapping order and therefore each type's default track.

combined also retains chapters, arbitrary container tags, and every attachment from the source. video-to-combined carries that source-side data with the video. mux uses the video's global metadata and chapters and unions attachments from both operands.

Metadata, chapters, and attachments

Operation	Signature	Description
set-language	TRACK STRING -> TRACK	Set a video, audio, or subtitle language tag.
set-title	TRACK STRING -> TRACK	Set a video, audio, or subtitle title.
set-default	TRACK BOOL -> TRACK	Set or clear its default disposition.
set-forced	TRACK BOOL -> TRACK	Set or clear its forced disposition.
chapter	START END STRING -> CHAPTER	Construct a chapter; END must be after START.
add-chapter	COMBINED CHAPTER -> COMBINED	Append a chapter.
drop-chapter	COMBINED INDEX -> COMBINED	Remove a chapter.
move-chapter	COMBINED FROM TO -> COMBINED	Reorder chapters.
add-attachment	COMBINED ATTACHMENT -> COMBINED	Append an external attachment.
drop-attachment	COMBINED INDEX -> COMBINED	Remove an attachment.
move-attachment	COMBINED FROM TO -> COMBINED	Reorder attachments.
set-tag	COMBINED KEY VALUE -> COMBINED	Set or replace a global container tag.

Track metadata follows its track through indexed and timeline operations. Existing disposition flags such as hearing-impaired, visual-impaired, commentary, and original are preserved. Timeline operations clip, rebase, shift, or scale chapters with the media. Concatenation keeps the left container tags, appends right chapters at the left duration, and unions attachments. Attachments currently require Matroska output.

Time and stream editing

Timeline operations accept bare tracks and combined values. On a combined value they transform every video, audio, and subtitle track together.

Operation	Signature	Description
length	VIDEO -> DURATION	Push the known video duration.
	AUDIO -> DURATION	Push the known audio duration.
	COMBINED -> DURATION	Push the longest known contained-track duration.
	SUBTITLES -> DURATION	Push the known subtitle duration.
slice	VIDEO START LENGTH -> VIDEO	Keep LENGTH beginning at START and reset timestamps.
	AUDIO START LENGTH -> AUDIO	Audio form of slice.
	SUBTITLES START LENGTH -> SUBTITLES	Subtitle form of slice.
	COMBINED START LENGTH -> COMBINED	Slice every contained track.
take	VIDEO LENGTH -> VIDEO	Keep at most the first LENGTH.
	AUDIO LENGTH -> AUDIO	Audio form of take.
	SUBTITLES LENGTH -> SUBTITLES	Subtitle form of take.
	COMBINED LENGTH -> COMBINED	Take from every contained track.
concat	VIDEO VIDEO -> VIDEO	Append the second video to the first.
	AUDIO AUDIO -> AUDIO	Append the second audio to the first. Mixed types are rejected.
	SUBTITLES SUBTITLES -> SUBTITLES	Append subtitle timelines.
	COMBINED COMBINED -> COMBINED	Concatenate corresponding tracks by type and index.
delay	VIDEO DURATION -> VIDEO	Shift video timestamps later.
	AUDIO DURATION -> AUDIO	Insert an audio delay.
	SUBTITLES DURATION -> SUBTITLES	Shift subtitle timestamps later.
	COMBINED DURATION -> COMBINED	Delay every contained track.

length fails at compilation if no duration can be determined. Source durations come from ffprobe; edited durations are propagated without creating temporary media.

Combined concatenation requires equal video, audio, and subtitle counts on both operands. Subtitle codecs are handled internally as plain text, ASS/SSA, or bitmap (PGS, DVD/VobSub, DVB, XSUB). Untouched compatible streams are mapped with stream copy. Edited text stays text, edited ASS/SSA stays ASS, and edited bitmap subtitles use Matroska intermediates with stream copy. Subtitle concat requires matching codecs. ASS cue ends are clipped exactly after slice and take; bitmap timing is packet-based. ASS/SSA and bitmap subtitles require Matroska output (standalone ASS is also accepted) rather than being silently converted to a lossy or incompatible representation.

Subtitle burning

Operation	Signature	Description
burn-subtitles	VIDEO SUBTITLES -> VIDEO	Burn text subtitles using renderer defaults.
	VIDEO SUBTITLES BURN_STYLE -> VIDEO	Burn text subtitles using explicit appearance settings.

Burning accepts VIDEO, not COMBINED; extract or take a video track first. Plain text and ASS/SSA are supported. Bitmap subtitle codecs such as PGS, DVD, DVB, and XSUB are rejected. Font attachments found beside the subtitle stream are extracted into a temporary libass font directory. A burn-style is a semicolon-separated list containing:

Property	Values
font	A font-family name.
size	A positive font size.
color	#RGB, #RRGGBB, or #RRGGBBAA.
outline-color	A color in the same formats.
outline-width	A non-negative width.
shadow	A non-negative shadow depth.
align	top-left, top-center, top-right, center-left, center, center-right, bottom-left, bottom-center, or bottom-right.
margin	A non-negative vertical margin.

Unknown properties and malformed values fail during compilation. Styles are translated to validated libass overrides; raw ASS syntax is not accepted. On ASS/SSA, inline override tags remain part of the subtitle events.

Audio operations

Operation	Signature	Description
volume	AUDIO SCALAR -> AUDIO	Multiply audio volume by the scalar.
mix	AUDIO AUDIO -> AUDIO	Mix two streams; the result lasts as long as the longer input.
silence	DURATION -> AUDIO	Generate stereo 48 kHz silence of the requested duration.

Speed and fades

Operation	Signature	Description
speed	VIDEO SCALAR -> VIDEO	Change video speed using timestamps.
	AUDIO SCALAR -> AUDIO	Change audio speed using one or more atempo stages.
	SUBTITLES SCALAR -> SUBTITLES	Scale subtitle timestamps.
	COMBINED SCALAR -> COMBINED	Change every contained track's speed.
fade-in	VIDEO DURATION -> VIDEO	Fade video in from the start.
	AUDIO DURATION -> AUDIO	Fade audio in from the start.
fade-out	VIDEO DURATION -> VIDEO	Fade video out over the final duration.
	AUDIO DURATION -> AUDIO	Fade audio out over the final duration.

Speed must be greater than zero. Fades preserve stream duration. fade-out requires a known input duration so its start time can be calculated.

Arithmetic and comparisons

Operation	Signature	Description
add	SCALAR SCALAR -> SCALAR	Add scalars.
	DURATION DURATION -> DURATION	Add durations.
sub	SCALAR SCALAR -> SCALAR	Subtract the right scalar from the left.
	DURATION DURATION -> DURATION	Subtract durations; a negative result is rejected.
mul	SCALAR SCALAR -> SCALAR	Multiply scalars.
	DURATION SCALAR -> DURATION	Scale a duration.
div	SCALAR SCALAR -> SCALAR	Divide scalars.
	DURATION SCALAR -> DURATION	Divide a duration by a scalar.
eq, ne	T T -> BOOL	Test equality or inequality for matching SCALAR, DURATION, or BOOL values.
lt, le, gt, ge	T T -> BOOL	Compare matching SCALAR or DURATION values.
and, or	BOOL BOOL -> BOOL	Boolean conjunction or disjunction.
not	BOOL -> BOOL	Boolean negation.

T must be the same type on both sides. Media values are not comparable. Division by zero, non-finite arithmetic, and negative duration results are rejected.

Conditionals

Conditionals use structured if, optional else, and end markers:

video "$1"
dup
length
duration 10s
gt
if
  duration 10s
  take
else
  # The original video remains unchanged.
end

if consumes a BOOL. Both branches begin with the same remaining stack and must leave identical stack types. Both branches are typechecked, but only the selected branch is compiled, probed, and added to the FFmpeg graph. Omitting else is equivalent to an empty false branch, so the true branch must preserve the stack shape in that case.

Conceptually, if both branches transform S into T:

S BOOL if ... else ... end -> T

Unrollable loops

Loops use Forth-style begin, while, and repeat markers:

video "$1"
scalar 0
begin
  dup
  scalar 3
  lt
while
  swap
  duration 1s
  take
  swap
  scalar 1
  add
repeat
drop

At begin, let the current stack shape be S. The condition section must transform S into S BOOL. while consumes that Boolean. The body must transform S back into exactly S before repeat. When the condition becomes false, the loop leaves S on the stack.

Loops execute during compilation and are fully unrolled into the FFmpeg graph. Consequently, every condition must be computable from literals, arithmetic, Boolean operations, and known probed media durations. There is no frame-time or sample-time control flow. A loop that attempts more than 10,000 iterations is rejected.

Programme result

A valid programme must leave exactly one VIDEO, AUDIO, SUBTITLES, or COMBINED value on the stack. Helper values such as BURN_STYLE, STRING, CHAPTER, ATTACHMENT, DURATION, INDEX, SCALAR, and BOOL cannot be final results. A combined result maps every track in per-type collection order.

Final FFmpeg encoding arguments

By default, final video and audio streams use -c:v libx264 -c:a aac.

Instruction	Effect
encoding "-c:v libx265 -crf 18 -c:a libopus"	Replace the complete default video/audio encoding argument vector. A later encoding overwrites the earlier one.
ffmpeg-args "-movflags +faststart"	Append final FFmpeg output arguments. Repeated calls accumulate in programme order.

The strings are split on whitespace without shell evaluation. Single-quoted groups inside the outer double-quoted language literal form one argument, for example ffmpeg-args "-metadata comment='processed episode'". Empty encoding "" suppresses the default video/audio codec arguments entirely. Appended arguments are placed immediately before the output path, so advanced users may deliberately override earlier FFmpeg options. Both instructions are compile-time configuration and do not consume or produce stack values. Their results appear in -n output. Subtitle codec selection, mapping, metadata, chapters, and attachments remain compiler-managed unless appended arguments explicitly supersede an FFmpeg option.