Caption Cue Centered Gap Placement
Center an integer-duration caption inside a supplied gap; odd leftover milliseconds place the extra millisecond on the right.
Description
Center an integer-duration caption inside a supplied gap; odd leftover milliseconds place the extra millisecond on the right.
Centering a cue in an integer-millisecond gap can leave one extra millisecond on one side.
When to use this tool
Center an integer-duration caption inside a supplied gap; odd leftover milliseconds place the extra millisecond on the right.
- Prepare the supplied gapStart, gapEnd, duration fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter gapStart, gapEnd, duration. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.start, result.end, result.leftMargin, result.rightMargin. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Require an ordered gap and duration fitting it. Put start at gapStart plus floor((gap length minus duration)/2), then return end and both margins.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| gapStart | gap start. | Integer from 0 to 1e12 inclusive |
| gapEnd | gap end. | Integer from gapStart to 1e12 inclusive |
| duration | duration. | Integer from 0 to gapEnd - gapStart inclusive |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.start | The start value under the stated formula or text convention. |
| result.end | The end value under the stated formula or text convention. |
| result.leftMargin | The left margin value under the stated formula or text convention. |
| result.rightMargin | The right margin value under the stated formula or text convention. |
{
"input": {
"gapStart": 10,
"gapEnd": 21,
"duration": 4
},
"output": {
"result": {
"start": 13,
"end": 17,
"leftMargin": 3,
"rightMargin": 4
}
}
}Limitations and assumptions
- Any odd spare millisecond goes to the right margin. The tool does not check surrounding real cues or choose a duration.
- Input cue records contain string id/text and integer millisecond start/end from zero to one trillion, with end at least start. At most 128 cue records are accepted; IDs need not be unique.
- Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
- Lists are limited to 128 entries. JSON text must meet bounded size and depth checks, and numeric outputs beyond the safe finite magnitude are rejected. Exact large integers use decimal strings.
- Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.
Alternative or Complementary methods
Use a subtitle-format parser or media review for markup, file syntax and synchronization. Preserve the integer-millisecond timeline and the stated overlap or clipping convention when composing these operations.
References
Similar or alternative tools
- Caption Cue Gap Table
Report signed adjacent caption timing gaps in sorted start order; negative gaps retain overlap evidence.
- Caption Adjacent Identical Merger
Merge adjacent sorted cues with exact identical text only when touching or overlapping; retain all contributing IDs.