Step 1: Provide your MP4 files using the button above or by toss and let go.
Step 2: Click the 'Convert' button to start the conversion.
Step 3: Fetch your converted FLV files.
MP4 to FLV Conversion FAQ
How do I convert MP4 to FLV without re-encoding the video stream?
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When the MP4 and FLV containers can both carry the same codec (H.264, H.265, VP9, AV1), the converter falls back to a remux: the elementary streams are copied byte-for-byte into the FLV container and only the wrapper changes. A remux of a 1 GB MP4 into FLV typically finishes in 5-15 seconds with zero quality loss. Almost every MP4 in the wild is H.264 video with AAC audio; the container also legally holds HEVC, AV1 and VP9. FLV typically holds Sorenson Spark or H.264 video with MP3 or AAC audio, wrapped in a stream format designed for RTMP delivery.
What happens to the subtitle tracks in my MP4 file?
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They cannot stay selectable, because FLV has no soft-subtitle stream to hold them. There are two ways out: burn them into the video during conversion, which makes them permanent and unstyleable, or export them as a separate .srt alongside the FLV for the player to load. The converter tells you which it did rather than dropping them silently. No current browser, phone or TV can play FLV — anything still in this container has to be moved out of it to remain watchable.
Can I still embed the file on a web page after converting MP4 to FLV?
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Not directly. MP4 plays inline in every browser; FLV does not, so a page embedding it falls back to a download link or an empty player frame. If the file is destined for a website, keep the MP4 for the web and treat the FLV as the archive or editing copy.
Will the FLV still play smoothly on a phone or a TV?
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It may not. MP4 is decoded by dedicated silicon on phones, tablets and TVs, which is why it plays without flattening the battery. FLV typically falls back to software decoding on the same hardware — higher CPU load, a warmer device, and dropped frames on 4K material. For a device target, MP4 is the safer container to stay in.
What happens to 5.1 surround audio when converting MP4 to FLV?
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It is downmixed to stereo, because FLV has no dependable multichannel path. The fold-down uses the standard ITU coefficients so dialogue in the centre channel stays intelligible and the surrounds come in at reduced level rather than vanishing. Anything that relied on discrete channel placement is gone after that.
Why would I convert MP4 to an older format like FLV?
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Because a lot of hardware never learned anything newer and never will. DVD players, in-car head units, camcorder playback modes, industrial displays and plenty of broadcast ingest equipment accept FLV and nothing else. The conversion is a deliberate step down in efficiency, bought in exchange for working on a device that has no other option. FLV’s low per-packet overhead made it excellent at streaming over the unreliable connections of its era, and huge archives of it still exist.
Will multi-track audio survive MP4 to FLV conversion?
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Yes — every audio track in the MP4 (director commentary, alternate languages, descriptive audio) is preserved in the FLV when the target container supports multi-stream audio. MKV and MOV handle unlimited audio tracks; MP4 supports many but some hardware players only see track 1; WebM is capped at one Opus / Vorbis track. FLV is the Flash Video container that carried essentially all web video from roughly 2003 until Flash was switched off at the end of 2020.
Are subtitle tracks preserved when converting MP4 to FLV?
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Soft subtitles (selectable tracks) survive when FLV can carry them: MKV holds SRT, ASS, SSA, PGS, VobSub natively; MP4 only holds mov_text (a stripped-down format). Converting an MKV with ASS styled subs to MP4 will typically downgrade them to mov_text or burn them in. Hardsubs (burned into the video) carry over regardless.
Does MP4 to FLV keep chapter markers / DVD-style navigation?
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Chapter metadata transfers between MP4 and FLV whenever both containers support a chapter atom (MKV, MP4, MOV). WebM stores chapters in a Matroska-compatible block, so MKV <-> WebM chapters round-trip cleanly. AVI has no chapter spec at all, so an AVI source arrives with no chapters to carry across and an AVI target cannot store the ones it was handed; add markers manually afterwards if you need them.
What about MKV attachments (fonts, cover art) when going MP4 to FLV?
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MKV is the only mainstream container that stores arbitrary attached files (TTF fonts for ASS subs, JPG cover art, fan-translated PDF inserts). Going from MP4 to FLV drops these attachments when FLV is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep MP4 as a backup if you depend on attached fonts.
Which codec does the FLV output use by default?
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The default codec is chosen to match the FLV container conservatively: MKV defaults to H.265 (HEVC) for better compression; MP4 defaults to H.264 for the widest device support; WebM defaults to VP9; AVI uses MPEG-4 ASP (DivX/Xvid lineage). Override via the advanced codec dropdown — AV1 is available for MKV / WebM where you want maximum compression and can wait through the encode.
How does HDR (HDR10, Dolby Vision) survive MP4 to FLV?
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HDR static metadata (HDR10 mastering display values, max content light level) carries through to FLV when both containers and the chosen codec support it (HEVC, AV1 in MKV / MP4). Dolby Vision is more fragile — DV profile 5 / 7 / 8.1 in MP4 commonly survives only into MKV with HEVC; converting to an FLV container that does not carry the DV layer flattens to HDR10.
