Step 1: Provide your FLV 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 MP4 files.
FLV to MP4 Conversion FAQ
How do I convert FLV to MP4 without re-encoding the video stream?
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When the FLV and MP4 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 MP4 container and only the wrapper changes. A remux of a 1 GB FLV into MP4 typically finishes in 5-15 seconds with zero quality loss.
Will multi-track audio survive FLV to MP4 conversion?
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Yes — every audio track in the FLV (director commentary, alternate languages, descriptive audio) is preserved in the MP4 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.
Are subtitle tracks preserved when converting FLV to MP4?
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Soft subtitles (selectable tracks) survive when MP4 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 FLV to MP4 keep chapter markers / DVD-style navigation?
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Chapter metadata transfers between FLV and MP4 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, so converting AVI to MP4 produces an unchaptered file unless you add markers manually.
What about MKV attachments (fonts, cover art) when going FLV to MP4?
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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 FLV to MP4 drops these attachments when MP4 is not MKV — the elementary streams convert, but the attached payload stays in the source. Keep FLV as a backup if you depend on attached fonts.
Which codec does the MP4 output use by default?
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The default codec is chosen to match the MP4 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 FLV to MP4?
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HDR static metadata (HDR10 mastering display values, max content light level) carries through to MP4 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 FLV commonly survives only into MKV with HEVC; converting to a MP4 container that does not carry the DV layer flattens to HDR10.
Will the FLV to MP4 converter keep variable framerate (VFR)?
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MKV and WebM record real per-frame timestamps and handle VFR natively, so FLV VFR survives into a MP4 of those formats with no resampling. MP4 nominally stores timestamps too but some players assume CFR; the converter exposes a "force CFR" toggle that resamples VFR FLV to 24 / 30 / 60 fps MP4 for problematic targets.
Why is my MP4 file smaller / larger than the FLV after conversion?
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Same-codec remux produces a near-identical size (container overhead differs by 0.1-2%). A codec change can swing the size by 50% or more: H.264 to H.265 typically halves the file at the same visual quality; H.264 to AV1 halves it again on a slow preset. Going from a high-bitrate FLV (Blu-ray rip) to a low-bitrate MP4 (web upload) is the most common reason for a dramatic drop.
Does the FLV to MP4 converter handle 4K / 8K / 60fps content?
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Yes up to 8K (7680x4320) on Premium. Free tier handles 4K (3840x2160) up to the 1 GB file cap. Pure remuxes (same-codec passthrough) of large FLV into MP4 are limited by disk I/O, not CPU — a 30 GB FLV typically remuxes to MP4 in under a minute regardless of resolution. Re-encodes scale with pixel count.
Is my FLV file private during MP4 conversion?
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Yes — uploaded FLV files are processed in isolated workers and deleted within minutes of completion. We never view, store, retain, or share the content. See /privacy/ for the data retention window. The conversion pipeline runs on hardware we control end-to-end; no third-party APIs receive your file.
Can I trim, crop, or join FLV files during the MP4 conversion?
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Not in the same job — keep conversion focused on container / codec. Use /trim/ to clip the FLV first, then queue the FLV -> MP4 step. For joining several clips into one MP4, the /merge/ tool stitches them on a per-codec basis (it remuxes when the inputs share a codec, re-encodes otherwise) and emits a single MP4 file at the end.
FLV (Flash Video) is a video container format developed by Adobe. It is commonly used for online video streaming and is supported by Adobe Flash Player.