# Change video speed

- Human page: https://happytails.ai/en/media-tools/change-video-speed/
- Markdown: https://happytails.ai/en/media-tools/change-video-speed.md
- Structured JSON: https://happytails.ai/agents/en/media-tools/change-video-speed/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `change-video-speed` |
| Category | media-tools |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser or server |
| HTTP API | /api/v1/tools/change-video-speed/run |
| Browser-agent interface | run_current_tool |

### Implementation notes

Browser processing keeps files on this device. Choosing Local server sends files to this website’s own processor. Adjusts video timing and audio speed together, preserving audio pitch.

### Inputs and settings

No free-text input is required. Use the file inputs and/or settings below.

Accepted browser files: `.mp4,.mov,.mkv,.webm,.avi`. Choose one file.

Browser file-input limit: 20971520 bytes in total. HTTP limits can differ.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `speed` | Speed multiplier | number | 1.25 | min=0.5 max=2 step=any |
| `engine` | Processing location | select | "browser" | Allowed: browser, server |

### HTTP contract

API calls process supplied data on the server. The website origin is `https://happytails.ai`. Server API hosting is not connected on the public website yet. Use your local server origin to test these requests.

```http
POST https://happytails.ai/api/v1/tools/change-video-speed/run
Content-Type: application/json
```

[Detailed operation reference](https://happytails.ai/en/api/tools/change-video-speed.md) · [Shared API guide](https://happytails.ai/en/api.md)

#### Limits

| Limit | Value |
| --- | --- |
| request_bytes | 31457280 |
| input_characters | 1000000 |
| files_bytes | 20971520 |
| max_files | 1 |
| timeout_seconds | 90 |

#### Complete input schema

```json
{
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "input": {
      "type": "string",
      "maxLength": 1000000,
      "default": "",
      "description": "Plain text input. File tools use files instead unless otherwise documented."
    },
    "options": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "speed": {
          "type": "number",
          "description": "Speed multiplier",
          "default": 1.25,
          "minimum": 0.5,
          "maximum": 2
        },
        "engine": {
          "type": "string",
          "description": "Processing location",
          "default": "browser",
          "enum": [
            "browser",
            "server"
          ]
        }
      }
    },
    "files": {
      "type": "array",
      "maxItems": 1,
      "items": {
        "type": "object",
        "required": [
          "name",
          "base64"
        ],
        "additionalProperties": false,
        "properties": {
          "name": {
            "type": "string",
            "maxLength": 200,
            "description": "Filename only, no path."
          },
          "mime": {
            "type": "string",
            "maxLength": 150
          },
          "bytes": {
            "type": "integer",
            "minimum": 0,
            "description": "Optional decoded byte count; must match content if supplied."
          },
          "base64": {
            "type": "string",
            "contentEncoding": "base64",
            "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
          }
        }
      }
    }
  }
}
```

#### Complete output schema

```json
{
  "type": "object",
  "required": [
    "tool",
    "result"
  ],
  "properties": {
    "tool": {
      "type": "string"
    },
    "result": {
      "type": "object",
      "required": [
        "text",
        "files"
      ],
      "properties": {
        "text": {
          "type": [
            "string",
            "null"
          ]
        },
        "data": {
          "description": "Parsed JSON when the textual result is JSON."
        },
        "name": {
          "type": "string"
        },
        "mime": {
          "type": "string"
        },
        "files": {
          "type": "array",
          "items": {
            "type": "object",
            "required": [
              "name",
              "mime",
              "bytes",
              "base64"
            ],
            "properties": {
              "name": {
                "type": "string"
              },
              "mime": {
                "type": "string"
              },
              "bytes": {
                "type": "integer"
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64"
              }
            }
          }
        }
      }
    }
  }
}
```

#### Error and retry handling

Failures return a non-200 status and `error.code` plus `error.message`. Correct invalid input before retrying; retry server-busy responses with bounded backoff. Returned files contain Base64 data, not persistent download URLs. Decode and inspect the output before treating conversion as successful. See the shared API guide for the complete status and timeout rules.

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

Video/audio timebase alignment and pitch behavior; preview duration.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "change-video-speed",
  "category": "media-tools",
  "built": true,
  "requirements": "Video/audio timebase alignment and pitch behavior; preview duration.",
  "implementation": {
    "fields": [
      {
        "key": "speed",
        "label": "Speed multiplier",
        "value": 1.25,
        "type": "number",
        "min": 0.5,
        "max": 2,
        "step": "any"
      },
      {
        "key": "engine",
        "label": "Processing location",
        "type": "select",
        "value": "browser",
        "values": [
          "browser",
          "server"
        ],
        "labels": {
          "browser": "Browser (files stay here)",
          "server": "Local server (larger files)"
        }
      }
    ],
    "files": true,
    "accept": ".mp4,.mov,.mkv,.webm,.avi",
    "multiple": false,
    "input": false,
    "processing": "Browser or server",
    "native": true,
    "maxFileBytes": 20971520,
    "note": "Browser processing keeps files on this device. Choosing Local server sends files to this website’s own processor. Adjusts video timing and audio speed together, preserving audio pitch.",
    "hybrid": true,
    "experience": {
      "automatic": false,
      "single": false,
      "label": "Your text",
      "placeholder": "Type or paste your input…",
      "help": "Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "POST /api/v1/tools/change-video-speed/run",
  "api": {
    "id": "change-video-speed",
    "name": "Change video speed",
    "category": "media-tools",
    "description": "Speed up or slow down a video and its audio.",
    "notes": "Browser processing keeps files on this device. Choosing Local server sends files to this website’s own processor. Adjusts video timing and audio speed together, preserving audio pitch.",
    "human_path": "/en/media-tools/change-video-speed/",
    "method": "POST",
    "endpoint": "/api/v1/tools/change-video-speed/run",
    "schema_url": "/api/v1/tools/change-video-speed",
    "input_schema": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "input": {
          "type": "string",
          "maxLength": 1000000,
          "default": "",
          "description": "Plain text input. File tools use files instead unless otherwise documented."
        },
        "options": {
          "type": "object",
          "additionalProperties": false,
          "properties": {
            "speed": {
              "type": "number",
              "description": "Speed multiplier",
              "default": 1.25,
              "minimum": 0.5,
              "maximum": 2
            },
            "engine": {
              "type": "string",
              "description": "Processing location",
              "default": "browser",
              "enum": [
                "browser",
                "server"
              ]
            }
          }
        },
        "files": {
          "type": "array",
          "maxItems": 1,
          "items": {
            "type": "object",
            "required": [
              "name",
              "base64"
            ],
            "additionalProperties": false,
            "properties": {
              "name": {
                "type": "string",
                "maxLength": 200,
                "description": "Filename only, no path."
              },
              "mime": {
                "type": "string",
                "maxLength": 150
              },
              "bytes": {
                "type": "integer",
                "minimum": 0,
                "description": "Optional decoded byte count; must match content if supplied."
              },
              "base64": {
                "type": "string",
                "contentEncoding": "base64",
                "description": "File bytes as padded base64. Use the tool-specific limits.files_bytes value for the total decoded input size."
              }
            }
          }
        }
      }
    },
    "output_schema": {
      "type": "object",
      "required": [
        "tool",
        "result"
      ],
      "properties": {
        "tool": {
          "type": "string"
        },
        "result": {
          "type": "object",
          "required": [
            "text",
            "files"
          ],
          "properties": {
            "text": {
              "type": [
                "string",
                "null"
              ]
            },
            "data": {
              "description": "Parsed JSON when the textual result is JSON."
            },
            "name": {
              "type": "string"
            },
            "mime": {
              "type": "string"
            },
            "files": {
              "type": "array",
              "items": {
                "type": "object",
                "required": [
                  "name",
                  "mime",
                  "bytes",
                  "base64"
                ],
                "properties": {
                  "name": {
                    "type": "string"
                  },
                  "mime": {
                    "type": "string"
                  },
                  "bytes": {
                    "type": "integer"
                  },
                  "base64": {
                    "type": "string",
                    "contentEncoding": "base64"
                  }
                }
              }
            }
          }
        }
      }
    },
    "processing": "Server; self-hosted native engine, no external conversion service",
    "limits": {
      "request_bytes": 31457280,
      "input_characters": 1000000,
      "files_bytes": 20971520,
      "max_files": 1,
      "timeout_seconds": 90
    }
  },
  "agent_processing": "Server; self-hosted native engine, no external conversion service",
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Speed up or slow down a video and its audio.

## Useful next steps

- [MP4 to MP3](https://happytails.ai/en/media-tools/mp4-to-mp3/): Convert MP4 files to MP3 with the available format settings. ([Markdown](https://happytails.ai/en/media-tools/mp4-to-mp3.md))

- [WAV to MP3](https://happytails.ai/en/media-tools/wav-to-mp3/): Convert WAV files to MP3 with the available format settings. ([Markdown](https://happytails.ai/en/media-tools/wav-to-mp3.md))

- [M4a to MP3](https://happytails.ai/en/media-tools/m4a-to-mp3/): Convert M4A files to MP3 with the available format settings. ([Markdown](https://happytails.ai/en/media-tools/m4a-to-mp3.md))

## How to use Change video speed

1. Choose a file in MP4, MOV, MKV, WEBM or AVI.
2. Review the settings, then choose Run Change video speed.
3. Review the result, then use Copy result or a download link when available.

## What to expect

Speed up or slow down a video and its audio. Browser processing keeps files on this device. Choosing Local server sends files to this website’s own processor. Adjusts video timing and audio speed together, preserving audio pitch.