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ffmpeg-mcp-server

by Ashutos1997
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extract_thumbnail

Capture a still image from a video at a chosen timestamp and return its saved path plus base64 data for vision model inspection.

Instructions

Capture a single still image from a video. Returns the saved image path and inlined base64 image data so vision models can inspect the frame.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
inputPathYesPath to the source video file.
timestampNoTimestamp to capture, such as '00:00:05', '10', or 'midpoint' for the middle frame. Default: '00:00:01'.
outputPathYesDestination image path ending in .png or .jpg (e.g. './thumb.png').
resolutionNoOptional scaled size formatted as 'WIDTHxHEIGHT', such as '1280x720'. Defaults to source resolution.
includeBase64NoReturn base64 image data in response for vision models. Default: true.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed5 schema fields changedv0.4.2
    • changedInput schema / properties / includeBase64 / description
      Previous value: -"Whether to include base64 image data in response for AI vision (default: true)"New value: +"Return base64 image data in response for vision models. Default: true."
    • changedInput schema / properties / inputPath / description
      Previous value: -"Path to the input video file"New value: +"Path to the source video file."
    • changedInput schema / properties / outputPath / description
      Previous value: -"Destination image file path (e.g. ./thumb.png or ./thumb.jpg)"New value: +"Destination image path ending in .png or .jpg (e.g. './thumb.png')."
    • changedInput schema / properties / resolution / description
      Previous value: -"Optional scaled resolution, e.g. '1280x720' or '640x360'"New value: +"Optional scaled size formatted as 'WIDTHxHEIGHT', such as '1280x720'. Defaults to source resolution."
    • changedInput schema / properties / timestamp / description
      Previous value: -"Timestamp to capture, e.g. '00:00:05', '10' (seconds), or 'midpoint' (calculates exact middle of video). Default: '00:00:01'."New value: +"Timestamp to capture, such as '00:00:05', '10', or 'midpoint' for the middle frame. Default: '00:00:01'."
  2. Changed1 schema field changedv0.3.0
    • addedInput schema / properties / includeBase64
      Added value: +{
+  "description": "Whether to include base64 image data in response for AI vision (default: true)",
+  "type": "boolean"
+}
  3. First observedv0.1.0

TDQS

A3.5/5.0
Behavior3/5

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

No annotations are provided, so the description carries the burden. It does disclose the response shape well – a saved file path plus inlined base64 for vision models – which is genuinely useful. However, it omits write semantics to outputPath (overwrite? create directories?), failure modes for invalid timestamps, and any size/cost implications of base64 inlining, which matters for a file-writing tool with zero annotation coverage.

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?

Two sentences, front-loaded with the action and then the return contract. Every clause earns its place and nothing is padded.

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

Completeness3/5

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

Purpose and return values are covered, which offsets the missing output schema. But with no annotations and a file-writing tool, the definition leaves gaps an agent needs: overwrite/directory behavior on outputPath, behavior on invalid or out-of-range timestamps, and the distinction from extract_keyframes.

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

Parameters3/5

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

Schema description coverage is 100%, so all five parameters including timestamp formats and resolution syntax are already documented in the schema. The description reinforces only the base64 return behavior and adds no new parameter semantics, so the baseline 3 applies.

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

Purpose4/5

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

States a specific verb and resource: 'Capture a single still image from a video,' which is unambiguous. It does not differentiate itself from the sibling extract_keyframes, so an agent must infer that this tool returns one frame while that one returns many.

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?

Usage is only implied by 'single still image' – there is no explicit statement of when to choose this over extract_keyframes, nor any prerequisite or exclusion (e.g. video-only input, overwrite behavior). The word 'single' is the only signal separating it from its closest sibling.

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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