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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There is no stream-copy switch on this page. A few pairs copy a compatible video stream into the FLV container without re-encoding it, MKV to MP4 among them, which is quick and loses no quality. Most pairs re-encode the video. 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 are dropped. FLV has no soft-subtitle stream to hold them, and the converter neither burns them into the picture nor exports them as a separate file. If you need them, extract the subtitles to an .srt file with a desktop tool such as ffmpeg or MKVToolNix before converting, and load that file alongside the FLV in your player. 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.
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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Usually not. Most conversions keep one audio track, the one with the most channels (normally the main mix), re-encoded for the FLV container, so commentary and alternate-language tracks are dropped. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every track, and so does MP4 to MOV. To keep a different track, remux the MP4 with that track first (VLC or ffmpeg can do this), then convert it. 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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On some pairs. MP4 to MOV keeps every text subtitle track. AVI, WMV, MPEG, FLV, VOB and M4V to MKV keep every subtitle track: text subtitles are copied or converted to SRT, and picture-based subtitles such as DVD or Blu-ray ones are copied as they are. MP4, MOV and WebM to MKV keep only the first subtitle track (as ASS), and MP4 to WebM keeps the first one as WebVTT. Other pairs, including MKV to MP4 or MOV and WebM to MP4, drop subtitle tracks, and the converter does not burn them into the picture. Subtitles that are already burned in stay, because they are part of the video frames.
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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It depends on the FLV container. MP4, MOV and MKV output use H.264, which plays on practically every phone, browser and TV. WebM output uses VP9. AVI, WMV and MPEG output use the older codecs those formats were designed for.
How does HDR (HDR10, Dolby Vision) survive MP4 to FLV?
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There is no HDR processing or tone mapping. When the video stream is copied (MKV to MP4 or MOV with the default settings), HDR10 passes through as it is. When the video is re-encoded, the HDR10 mastering metadata is dropped and Dolby Vision or HDR10+ data is not kept, and with a Quality, Resolution or Frame Rate setting some pairs also reduce the video to 8-bit colour, so an HDR MP4 can look washed out in the FLV.
