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Add or mix video audio

video_add_audio
Destructive

Add, replace, or mix an audio file into a video with control over volume, fade effects, and start time. Renders a new output file from local files.

Instructions

Add, replace, or mix an audio file into an existing video and render a new output file. The source video and audio are read only; output_path is created or overwritten. Controls volume, fade-in, fade-out, mix/replace mode, and optional start time.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
video_pathYesAbsolute path to an existing local video file. The input file is read only.
audio_pathYesAbsolute path to an existing local audio file such as MP3, WAV, M4A, or AAC.
volumeNoAudio gain from 0.0 to 2.0, where 1.0 preserves original loudness.
fade_inNoNon-negative fade-in duration in seconds applied to the inserted audio.
fade_outNoNon-negative fade-out duration in seconds applied near the inserted audio end.
mixNoTrue mixes the new audio with existing video audio; false replaces the original audio track.
start_timeNoOptional start offset in seconds where the inserted audio begins.
output_pathNoDestination video path. Auto-generated when omitted; an existing supplied path may be overwritten.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Behavior4/5

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

Annotations already mark destructiveHint=true, so description adds value by clarifying 'source video and audio are read only; output_path is created or overwritten'. This provides context about file safety and overwriting behavior beyond what annotations offer.

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 concise sentences with no wasted words. The first sentence defines the core action, and the second adds safety and feature details. Information is front-loaded and earns its place.

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

Completeness5/5

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

Given the tool's complexity (8 parameters, destructive hint, output schema exists), the description covers all essential behaviors (read-only sources, overwriting output, configurable options) without needing to describe return values due to presence of output schema.

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 the baseline is 3. The description only lists parameter names (volume, fade-in, etc.) without adding new information beyond the schema's parameter descriptions. No additional semantic meaning is provided.

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 clearly states the tool's purpose with a specific verb-resource combination: 'Add, replace, or mix an audio file into an existing video'. It lists configurable options (volume, fade, mix, start time) and distinguishes the action from similar tools like video_add_generated_audio by covering multiple modes.

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 description implies usage by listing functionality (add, replace, mix, volume, fade) but does not explicitly state when to use this tool over alternatives like video_add_generated_audio or video_extract_audio. No exclusions or conditions for use are provided.

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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