FLV to MP4 Converter

Convert FLV to MP4 online and see exactly what timed-stream transcoding changes, what MP4 still can't promise, and how to verify the result.

Choose Files or drop a video file here Preview it before choosing the output settings

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◈ Encrypted transfer◷ Short retention⊘ No watermark◎ Works on every device

Timed-stream transcoding: how FLV becomes MP4

The picture, sound, and timing streams inside FLV is decoded first, then re-encoded into MP4's own codec and container profile. Duration typically holds steady even as compression, channel mapping, frame cadence, or auxiliary streams shift underneath it. The FLV reader walks timestamped audio, video, and script-data tags, then identifies the legacy codecs and keyframe index before a modern stream is written. MP4 output organizes tracks around web-friendly sample timing and fast-start playback; captions, chapters, rotation, and any auxiliary streams remain separate preservation decisions.

Decoded from the legacy Flash Video container historically used for browser streaming. Encoded to an MPEG-4 container carrying H.264 video and AAC audio when both streams exist, built for broad device support.

INPUT MODEL

FLV

FLV video container

Used for moving images, timed audio, and playback metadata.

Family: Video
MIME: video/x-flv

→

OUTPUT MODEL

MP4

MPEG-4 video

Designed for widely compatible web and device video.

Family: Video
MIME: video/mp4

Reading FLV correctly and satisfying what MP4 expects

FLV

What can fail when FLV video container is interpreted

Current browsers no longer provide native Flash playback, and FLV may contain older codecs with limited hardware decoding.

MP4

What MPEG-4 video cannot safely promise

An audio-only source stays audio-only here — no picture gets generated — and side streams like captions are a separate preservation question.

ENGINE

How the MP4 writer handles this route

The verified MP4 profile uses H.264 video at CRF 23 and AAC audio at 192 kbit/s, with fast-start metadata.

Checking the MP4 result before you trust it

BEFORE

Record the FLV evidence before conversion

Inspect codecs, dimensions, frame rate, duration, audio sync, keyframe seeking, and the complete transcoded result.

AFTER

Test the MP4 file in its receiving workflow

Test that it plays and seeks correctly, that audio stays in sync, and that the video stream is actually present if you expected one.

Deciding when FLV to MP4 is the right conversion

Confirm the receiving player, editor, or publishing service actually names MP4's container and codecs before switching; stay with FLV if extra tracks or original encoding need to survive intact.

What changes between the FLV model and the MP4 deliverable

MP4 can hold a timed animation, but FLV has no frames to give it; expect a single still frame unless more source material is supplied.
The MP4 encoder can discard perceptual detail; the important test is the resulting image, motion, or sound - Not matching dimensions alone.
Treat FLV-specific metadata fields as optional in the MP4 result until you have actually confirmed they survived.