FLV to MP4 Converter

Convert FLV video files to MP4 format

Related Tags
Files 80 FFmpeg 28 Video 27 MP4 13

Convert FLV (Flash Video) files to MP4 format. FLV was widely used for web streaming but has been deprecated. MP4 is the modern standard with universal device and platform support.

Click to upload file or drag and drop file here

Maximum file size: 100MB

Only applies when re-encoding. 18-28 is recommended range

Key Facts

Category
Images, Audio & Video
Input Types
file, select, number
Output Type
file
Sample Coverage
4
API Ready
Yes

Overview

Easily convert legacy FLV (Flash Video) files into the modern, universally compatible MP4 format. This tool allows you to customize video and audio codecs, adjust CRF quality, or copy streams directly without re-encoding for fast, lossless conversion.

When to Use

  • •When you have legacy Flash Video (.flv) files that no longer play on modern web browsers, smartphones, or media players.
  • •When you need to import older video assets into modern editing software or upload them to streaming platforms that do not support the FLV format.
  • •When you want to compress old video files or change their codecs to H.264 or H.265 to improve storage efficiency and compatibility.

How It Works

  • •Upload your FLV video file, keeping within the 500 MB size limit.
  • •Select your preferred video and audio codecs, or choose 'Copy' to bypass re-encoding for instant conversion.
  • •Optionally set a CRF quality value between 0 and 51 to control the output file size and visual fidelity.
  • •Click convert to process the file and download your optimized MP4 video.

Use Cases

Archiving old website video assets originally encoded in Flash Video format to modern, future-proof MP4.
Converting legacy screen recordings or game captures saved as FLV so they can be edited in modern software like Premiere or DaVinci Resolve.
Optimizing video files for mobile playback by converting FLV to MP4 with H.264 and AAC codecs.

Examples

1. Lossless Legacy Video Migration

Digital Archivist
Background
An archivist has a library of historical web animations and clips saved in FLV format that need to be preserved in a modern container without losing any original quality.
Problem
Convert FLV files to MP4 container quickly without degrading the original video or audio streams.
How to Use
Upload the FLV file, set both Video Codec and Audio Codec to 'Copy (No Re-encoding)', and run the converter.
Example Config
Video Codec: copy, Audio Codec: copy
Outcome
The FLV container is swapped to MP4 instantly without re-encoding, preserving 100% of the original stream quality.

2. High-Efficiency Mobile Playback Optimization

Content Creator
Background
A creator has old tutorial videos in FLV format that they want to upload to social media platforms, requiring high compatibility and low file size.
Problem
Re-encode the video to H.265/HEVC with AAC audio to minimize file size while maintaining excellent visual quality.
How to Use
Upload the FLV file, select 'H.265/HEVC' for the Video Codec, 'AAC' for the Audio Codec, and set the CRF Quality to 22.
Example Config
Video Codec: libx265, Audio Codec: aac, CRF Quality: 22
Outcome
A highly compressed MP4 video file optimized for mobile streaming with excellent visual fidelity.

Try with Samples

audio, video, file
Video H.264 Samples
Sample video files encoded in H.264 (AVC) format
matched family video
video
WebRTC Real-Time Communication Samples
Comprehensive WebRTC samples for peer-to-peer audio/video communication, data channels, screen sharing, and signaling server implementation
matched family audio,video
audio, video
Video AV1 Samples
Sample video files encoded in AV1 format
matched family video
video
Video H.265 Samples
Sample video files encoded in H.265 (HEVC) format
matched family video
video

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FAQ

Can I convert FLV to MP4 without losing quality?

Yes. Set both the video and audio codecs to 'Copy' to extract and repackage the streams into an MP4 container without re-encoding, ensuring zero quality loss.

What is the maximum file size supported?

You can upload and convert FLV files up to 500 MB (524,288,000 bytes) in size.

Which video codec should I choose for maximum compatibility?

H.264 (libx264) combined with AAC audio is highly recommended, as it is supported by almost all modern devices, operating systems, and web browsers.

What does the CRF quality setting do?

Constant Rate Factor (CRF) controls video quality during re-encoding. Lower values yield higher quality but larger files; a range of 18 to 28 is recommended.

Does this tool support H.265/HEVC?

Yes, you can select H.265 (libx265) as the video codec to achieve better compression and smaller file sizes than H.264.

API Documentation

Request Endpoint

POST /en/api/tools/flv-to-mp4

Request Parameters

Parameter Name Type Required Description
videoFile file (Upload required) Yes -
videoCodec select No -
audioCodec select No -
quality number No Only applies when re-encoding. 18-28 is recommended range

File type parameters need to be uploaded first via POST /upload/flv-to-mp4 to get filePath, then pass filePath to the corresponding file field.

Response Format

{
  "filePath": "/public/processing/randomid.ext",
  "fileName": "output.ext",
  "contentType": "application/octet-stream",
  "size": 1024,
  "metadata": {
    "key": "value"
  },
  "error": "Error message (optional)",
  "message": "Notification message (optional)"
}
File: File

AI MCP Documentation

Add this tool to your MCP server configuration: 

{
  "mcpServers": {
    "elysiatools-flv-to-mp4": {
      "name": "flv-to-mp4",
      "description": "Convert FLV video files to MP4 format",
      "baseUrl": "https://elysiatools.com/mcp/sse?toolId=flv-to-mp4",
      "command": "",
      "args": [],
      "env": {},
      "isActive": true,
      "type": "sse"
    }
  }
}

You can chain multiple tools, e.g.: `https://elysiatools.com/mcp/sse?toolId=png-to-webp,jpg-to-webp,gif-to-webp`, max 20 tools.

Supports URL file links or Base64 encoding for file parameters.

If you encounter any issues, please contact us at [email protected]