How to use the FLV to MP4 converter
- Add the FLV or F4V files, or the folder they live in.
- Keep Quality at Balanced unless the source is especially small.
- Convert to MP4 and download.
Newer and older Flash video
FLVs from roughly 2008 onward usually contain H.264 picture with AAC sound. Those are rewrapped into MP4 nearly instantly, with no change to quality. Older files use Sorenson Spark or VP6 with MP3 sound; since MP4 players cannot handle those, both tracks get encoded as H.264 and AAC.
Encoding a small Sorenson clip is quick, often faster than it plays, because each frame is tiny. Larger VP6 files from video sites of that era take longer but are still handled on the same single-core engine.
Seeking and leftover metadata
Flash files captured from live streams sometimes have gaps or jumbled timestamps. Writing them into MP4 generally produces a file you can scrub through properly, something old Flash players often struggled with.
Cue points and other metadata added by Flash tools are not carried across; the MP4 holds only picture and sound.
Working through an archive
Drop a whole folder of FLVs and they are converted one by one, each listed with its size before and after. When the queue finishes, the ZIP button gives you everything in one download.
Because H.264 files finish almost at once and older ones need a full encode, time per file varies widely inside a batch.
Questions
Is F4V handled too?
Yes. F4V is Adobe’s MP4-like wrapper, so H.264 and AAC inside it are simply copied.
Will my file get smaller?
A rewrapped H.264 FLV stays about the same size. Sorenson and VP6 files usually shrink, because H.264 is more efficient.
Do I need Flash Player or a plug-in?
No. ffmpeg compiled to WebAssembly reads the FLV, so no plug-in is involved at any point.
Can I lower the resolution?
Yes, under More settings. That forces an encode even for H.264 files, and smaller videos are never scaled up.