Convert FLV to MP4
Convert Flash FLV videos to modern MP4 format. Free, in your browser, no file upload.
.flv · up to 100 MB
Why convert FLV to MP4
From Flash archive to modern video
Total privacy
The video is processed with FFmpeg.wasm in your browser. No FLV file ever leaves your device.
Quality preserved
H.264 maintains the visual quality of the original FLV with equal or smaller file size.
Universal compatibility
MP4 with H.264 and AAC plays on any device, platform, browser, and social network.
Instant after first load
FFmpeg.wasm downloads once and is cached. Subsequent conversions are immediate.
How it works
Three steps, no hassle
Upload your FLV file
Drag or select your .flv file. No registration or format restrictions.
Automatic conversion to MP4
FFmpeg.wasm re-encodes the video to H.264 with AAC audio in your browser. Nothing is uploaded to servers.
Download the MP4
Download the resulting MP4, ready to play on any modern device or platform.
FAQ
Got questions?
FLV (Flash Video) is a video container format developed by Macromedia (later Adobe) from 2002. It was the standard format for web video during the Flash era (2002–2015), used by YouTube, Vimeo, Dailymotion, and virtually all online video sites until the adoption of HTML5.
There are millions of FLV files in personal and corporate archives: videos downloaded from YouTube before 2012, content from Flash-era websites, screen recordings with old software, and videos from Chinese platforms (Youku, Bilibili) that still use FLV internally. They are valid files with valuable content that simply need to be updated to the current format.
Exactly. Adobe Flash Player was officially discontinued on December 31, 2020, and all modern browsers removed their support. However, the FLV file format is independent of the Flash player — it is simply a video container. .flv files are still perfectly valid video files; they just need a modern codec to play on any device.
The conversion requires H.264 re-encoding, which involves some compression loss. However, since original FLVs are typically encoded with H.263 or VP6 (older, less efficient codecs), the quality difference is minimal. H.264 can preserve the same visual quality with equal or smaller files.
Generally similar to or smaller than the original FLV. H.264 is significantly more efficient than Flash-era video codecs (H.263, Sorenson Spark, VP6), so the resulting MP4 can be up to 20–30% smaller while maintaining the same visual quality.
The most common sources are: old YouTube downloads (before 2012 videos were saved as FLV), videos from Flash-era websites that are no longer online, Chinese video platforms (Youku, Iqiyi, old Bilibili), corporate training and webinar archives, and archived content from Chinese social networks.
FLV/Flash history (Macromedia 2002), Flash Player end-of-life (2020), legacy video archive migration
FLV (Flash Video) was developed by Macromedia in 2002 as the native video format for Flash Player, the browser plugin that dominated web video for over a decade. When YouTube launched in 2005, it chose FLV as its distribution format. Until approximately 2012, virtually all online video was served as FLV: YouTube, Vimeo, Dailymotion, MySpace Video, and thousands of video sites used this format. The FLV container can encapsulate H.263, Sorenson Spark, VP6, or H.264 video, along with MP3, AAC, or ADPCM audio.
The transition of web video from Flash to HTML5 was gradual between 2010 and 2015. YouTube began serving HTML5 in 2010 and completed the transition in 2015. Steve Jobs's decision not to include Flash on the iPhone (2007) accelerated the decline. Adobe announced Flash Player's end-of-life in 2017, with a deadline of December 31, 2020. Since January 2021, no modern browser (Chrome, Firefox, Safari, Edge) supports Flash Player. However, the legacy in the form of .flv files on personal hard drives and corporate servers is enormous — estimated at hundreds of millions of files.
Technically, converting FLV to MP4 with FFmpeg involves demuxing the FLV container, decoding the video stream (H.263/VP6/H.264) and audio (MP3/AAC), re-encoding the video with libx264 (H.264) and audio with libfdk_aac or aac, and muxing everything into the MP4 container. The basic command is ffmpeg -i input.flv -c:v libx264 -c:a aac output.mp4. In cases where the FLV already contains H.264 internally, it is possible to do a stream copy (-c:v copy) to avoid re-encoding and preserve the original quality losslessly.