MP4 to FLV Converter

How to Convert MP4 to FLV Online

1. Upload Your MP4 File: Drag and drop or click "Add Files" to select an MP4 or M4V video. Batch is supported — upload several clips and each converts in parallel on our servers.
2. Pick Video Codec and Audio Codec: Default video codec is FLV1 (Sorenson Spark) — the original FLV codec, accepted by every RTMP server and Flash-era player. Switch to H.264 if your RTMP endpoint or downstream player expects it (Wowza, nginx-rtmp, FFmpeg-based ingest, OBS test servers all accept H.264-in-FLV). Default audio codec is AAC; MP3 is also widely supported in FLV streams.
3. Set Quality, Resolution, or Trim (Optional): Under Quality Preset, pick Highest / Very High / High / Medium / Low / Lowest, or switch to Specific file size, Constant Bitrate, Variable Bitrate, Constant Quality (CRF), or Constraint Quality. Under Video resolution, keep original, choose a Preset Resolution (2160p / 1440p / 1080p / 720p / 480p / 360p / 240p / 144p), set a Resolution Percentage, or enter custom Width × Height. Under Trim, pick Time Range and enter Start Time and Duration in seconds or HH:MM:SS.sss.
4. Convert and Download: Click Convert. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark, never shared. Download individually or as a ZIP.

Why Convert MP4 to FLV?

FLV (Flash Video) is the container Adobe launched on September 10, 2003 with Flash Player 7. Adobe ended Flash Player support on December 31, 2020 and began blocking Flash content on January 12, 2021, so FLV is no longer used for browser playback. The container, however, is still the de-facto wire format for RTMP ingest — the encoder-to-server leg of nearly every live stream in 2026. Common reasons to convert MP4 to FLV in 2026:

• RTMP live-stream ingest — RTMP carries video as FLV packets. Twitch, YouTube Live, Facebook Live, Kick, Restream, and most enterprise webcasting platforms still accept RTMP/RTMPS for the encoder-to-platform leg of a live stream. When you publish a pre-recorded MP4 to one of these ingest endpoints (via OBS "Media Source" loop, FFmpeg ffmpeg -re -i in.mp4 -f flv rtmp://..., or a hardware encoder), the source is muxed as FLV in flight.
• Self-hosted RTMP servers — nginx-rtmp, Wowza Streaming Engine, Ant Media, Red5, MonaServer, and SRS all accept FLV/RTMP as primary input. If you're spinning up a private streaming relay or restreaming MP4 archives to an HLS/DASH origin, FLV is the cleanest direct push format.
• HTTP-FLV playback chains — Some Asian streaming stacks (Bilibili, Douyin tools, internal CDNs) deliver FLV over HTTP for sub-second latency. The encoder-side asset still has to be FLV.
• Legacy CMS and digital-signage uploads — A small but real set of training portals, kiosk software, and broadcast control systems built between 2007 and 2015 only ingest FLV. The format outlived its consumer-playback era inside these closed systems.
• Archival migration — Recovering content from old Flash-based learning management systems, museum kiosks, or corporate intranet libraries often means re-muxing modern MP4 sources into FLV so the legacy player accepts them.
• Adobe Animate export workflow — Animate (the rebranded Flash Professional) still imports and exports FLV for use inside legacy SWF projects and AIR applications.

MP4 vs FLV — Format Comparison

FLV Codec Choice Quick Guide

If you want to go the other direction, see FLV to MP4. For other FLV inputs use MOV to FLV or MKV to FLV, and to clip an existing FLV without re-encoding see Trim FLV.

Frequently Asked Questions

Why would I convert MP4 to FLV in 2026 if Flash is dead?

Flash Player is dead, but the FLV container is not. RTMP, the protocol every major live-streaming platform still accepts for encoder ingest (Twitch, YouTube Live, Facebook Live, Kick), carries video as FLV-formatted packets. If you want to publish a pre-recorded MP4 to one of those ingest endpoints — for an unattended loop, a virtual camera replay, or a scheduled rebroadcast — you typically mux the MP4 into FLV and push with ffmpeg -re -i input.mp4 -c copy -f flv rtmp://.... Standalone playback is the use case that vanished; live-streaming ingest is the use case that remained.

Which video codec should I pick inside the FLV container?

It depends on the downstream system. For modern live-streaming ingest (Twitch, YouTube Live, Wowza, nginx-rtmp, OBS recording-to-file, FFmpeg piping), pick H.264 — that's what platforms expect today and what gives you the best quality per kbps. For legacy Flash media servers, digital signage built before 2012, or Adobe Animate import, pick FLV1 (Sorenson Spark) — it's the original FLV codec and the safest fallback. VP6 sits in between and is mostly useful for archival fidelity to mid-2000s content.

Will Twitch or YouTube Live accept this FLV file?

You don't upload an FLV file to either — both accept RTMP push, not FLV upload. The conversion is the first step: produce an FLV (or H.264-in-MP4) and stream it to the ingest endpoint with a tool like FFmpeg, OBS Studio (Media Source → Stream), or Restream. Twitch's ingest expects H.264 video + AAC audio in an FLV-formatted RTMP stream; YouTube Live's rtmp://a.rtmp.youtube.com/live2 expects the same. Use H.264 + AAC settings in the converter for direct compatibility.

What about RTMPS — does it still use FLV inside?

Yes. RTMPS is RTMP wrapped in TLS for transport security; the payload format inside is still FLV-tagged video and audio packets. Facebook Live now requires RTMPS for new ingest endpoints, and Twitch supports it on rtmps://live.twitch.tv/app/. The encoder/converter side doesn't change — produce H.264 + AAC inside FLV, and the streaming client handles the TLS wrapper.

Why is my FLV file the same size as the original MP4?

Because FLV is a container, not a codec. If you keep the same video codec (H.264) and the same bitrate, you're remuxing — moving the existing compressed bitstream from one container to another — so the size stays nearly identical. Size only changes if you transcode (switch codec, change bitrate, change resolution, or trim). To shrink output, pick Constant Quality (CRF) with a higher number (28-32) under File Compression, lower the resolution, or switch to a Specific File Size target.

Can I keep H.264 video and just change the container?

Yes. With Video Codec set to H.264 and a bitrate mode that matches your source (or Constant Quality at a comparable CRF), the conversion is effectively a container swap — the H.264 bitstream is repackaged from MP4 into FLV with no re-encoding. This is the same operation FFmpeg does with -c:v copy -c:a copy -f flv. It's the fastest path and preserves source quality exactly.

Can modern browsers or VLC play the FLV after conversion?

VLC, MPV, MPC-HC, FFplay, and any libavformat-based player open FLV files directly. Web browsers cannot play FLV natively — Chrome, Firefox, Edge, and Safari all dropped Flash Player support during 2020-2021, and no replacement plug-in exists. For browser playback, keep your file as MP4 or convert FLV back to MP4 with FLV to MP4.

Can I trim or shrink the video while converting?

Yes. Under Trim → Time Range, enter a Start Time and Duration in seconds (12.5) or HH:MM:SS.sss format (00:01:30.500). To shrink size, choose Specific file size and enter a target MB value, or pick Constant Quality and raise the CRF slider toward 30. To downscale, pick a Preset Resolution like 720p or 480p — useful when the RTMP ingest endpoint enforces a maximum resolution or your upstream bandwidth is limited.

Is there a file size or batch limit?

No fixed per-file cap and no batch quantity limit. Conversion happens on our servers, so the practical limit is the available memory of your device. Multi-GB 4K MP4 sources convert successfully on a typical 16 GB laptop. Batch jobs run in parallel — drop in a folder of MP4s and download the FLVs individually or as a ZIP.