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ffmpeg-mcp-server

ffmpeg-mcp-server

by Ashutos1997
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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add_subtitles

Embed SRT or VTT subtitles into MP4, MKV, or MOV video containers without re-encoding, adding labeled tracks for playback.

Instructions

Embed an SRT or VTT subtitle track into a video container (mov_text for MP4, srt for MKV) without re-encoding the video stream.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "videoPath": "<videoPath>",
      "subtitlesPath": "<subtitlesPath>",
      "outputPath": "<outputPath>"
    },
    "name": "add_subtitles"
  }
}

Input Schema

NameRequiredDescriptionDefault
titleNoSubtitle track label displayed in video playersEnglish
languageNoISO 639-2 three-letter language code (e.g. 'eng', 'spa', 'fra', 'deu')eng
videoPathYesPath to the source video file
outputPathYesTarget output video path (.mp4, .mkv, or .mov)
subtitlesPathYesPath to subtitle file (.srt or .vtt)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv0.5.1
    • addedInput schema / properties / language / pattern
      Added value: +"^[a-zA-Z]{2,4}$"
    • addedInput schema / properties / title / maxLength
      Added value: +100
  2. First observedv0.1.0

TDQS

A4.2/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations, the description carries the burden and usefully discloses that the video stream is not re-encoded and that subtitle codecs depend on the container: mov_text for MP4 and srt for MKV. It does not cover output-file overwrite behavior, audio handling, or failure cases, but the core behavioral traits are clearly stated.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single front-loaded sentence with no filler. The parenthetical codec detail is directly relevant and does not obscure the main action.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a five-parameter file-producing tool with no annotations or output schema, the description covers the essential operation, supported subtitle formats, codec mapping, and no-re-encoding behavior. Minor gaps remain around overwrite semantics and audio-stream handling, but they do not prevent correct invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is already 100%, so the parameter schema documents all five inputs. The description still adds meaning beyond the schema by explaining the container-specific subtitle codec mapping that affects outputPath behavior.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: embed an SRT or VTT subtitle track into a video container. It also distinguishes the operation from hard-burning by specifying that the video stream is not re-encoded and by naming container-specific subtitle codecs.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The embedding and no-re-encoding language implies when this tool is appropriate, especially versus burn_subtitles. However, it does not explicitly name the alternative or state when not to use this tool, so the routing guidance is only implied.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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