CONVERT MP4 → FLV (MP4 to FLV)
Fast, secure MP4 to FLV conversion. No registration required.
📈 Target Minimum File Size (Guaranteed ≥ KB)
Lossless JPEG Q100 + standard COM segment padding for government & exam portals
Tap to choose your file Drop files here or click to browse
Automatic format identification and lossless transcoding across 201+ formats.
Convert to:
Detecting available formats...
Target Max File Size:
Uploading...
Processing your file...
READY!
Download File
Your file is converted & verified! Unlock instant download:
One-time secure payment via Stripe (Apple Pay, Google Pay, Card). Zero recurring subscription.
🛡️ Verification Audit
- ✓
- ✓ sRGB Color Fidelity
- ✓
Continue with this converted file (0s zero re-upload):
Batch Conversion Ready!
Your file is converted & verified! Unlock instant download:
One-time secure payment via Stripe (Apple Pay, Google Pay, Card). Zero recurring subscription.
Need to convert larger files or bigger batches right now?
Unlock up to 1 GB & priority cloud queue with 1-click Stripe checkout (Apple Pay, Google Pay, Card):
HOW TO CONVERT MP4 → FLV
Drop the video file
Select a MP4 file. We read the container and stream descriptors to plan the conversion.
FFmpeg handles the repackage
When codecs align, FFmpeg rewraps the existing streams into a FLV container — no quality loss, near-instant finish.
Retrieve the FLV
The FLV download is ready in seconds for stream-copy jobs, minutes for full transcodes.
FLV (Flash Video) peaked as the dominant web video format between roughly 2005 and 2015, carried by YouTube, Vimeo, and every major video-sharing platform before the HTML5 transition made it obsolete. Converting MP4 to FLV today is almost always driven by one of three narrow scenarios: embedding video in legacy Flash-based applications that cannot consume H.264 inside an MPEG-4 container, populating old media server software such as Adobe Media Server or Wowza instances still serving FLV over RTMP, or recovering playback in embedded hardware (set-top boxes, kiosk players) whose firmware predates MPEG-4 Part 14. The conversion strips away the MPEG-4 container and rewraps the video, typically keeping H.264 video and re-wrapping audio as MP3 or AAC inside the FLV container. The resulting file will not open in any modern browser natively and requires either a SWF-based player or a legacy environment — this is not a format upgrade; it is deliberate downgrade for backward compatibility.
Why convert MP4 to FLV
The only practical reason to produce FLV in 2024 is compatibility with environments that cannot be updated. Flash-based LMS platforms, older streaming appliances, and SWF-based video players embedded in intranet portals sometimes accept only FLV over RTMP. If your MP4 file plays correctly in every target you actually care about, there is no benefit to converting — FLV has no quality advantage, smaller ecosystem support, and carries the operational cost of needing a legacy player runtime to decode it.
MP4 vs FLV — Technical specifications
Side-by-side comparison of the technical details.
MP4
- MIME type
- video/mp4
- Container
- ISO Base Media File Format (ISO/IEC 14496-12)
- Common video codecs
- H.264 (AVC), H.265 (HEVC), AV1, VP9
- Common audio codecs
- AAC, MP3, FLAC, Opus
- Max file size
- Practically ~16 TB; 2^63 bytes theoretical
- Streaming
- Supported with faststart (moov atom at front)
- MIME Type
- video/mp4
- Extension
- .mp4
- Category
- Video Files
- Full Name
- MP4 Video
- Conversion Engine
- FFMPEG
FLV
- MIME type
- video/x-flv
- MIME Type
- video/x-flv
- Extension
- .flv
- Category
- Video Files
- Full Name
- Flash Video
- Conversion Engine
- FFMPEG
- Extensions
- .flv, .f4v
- Video codecs
- Sorenson Spark, VP6, H.264 (F4V)
- Audio codecs
- MP3, Nellymoser, AAC
- Status
- Deprecated since December 31, 2020
| Specification | MP4 | FLV |
|---|---|---|
| MIME type | video/mp4 | video/x-flv |
| Container | ISO Base Media File Format (ISO/IEC 14496-12) | — |
| Common video codecs | H.264 (AVC), H.265 (HEVC), AV1, VP9 | — |
| Common audio codecs | AAC, MP3, FLAC, Opus | — |
| Max file size | Practically ~16 TB; 2^63 bytes theoretical | — |
| Streaming | Supported with faststart (moov atom at front) | — |
| MIME Type | video/mp4 | video/x-flv |
| Extension | .mp4 | .flv |
| Category | Video Files | Video Files |
| Full Name | MP4 Video | Flash Video |
| Conversion Engine | FFMPEG | FFMPEG |
| Extensions | — | .flv, .f4v |
| Video codecs | — | Sorenson Spark, VP6, H.264 (F4V) |
| Audio codecs | — | MP3, Nellymoser, AAC |
| Status | — | Deprecated since December 31, 2020 |
MP4 vs FLV — Strengths and limitations
What each format does best, and where it falls short.
MP4 Strengths
- Universal playback — every browser, phone, TV, game console, and editing suite reads MP4.
- Supports modern codecs (H.264, H.265, AV1) with no container changes.
- Progressive streaming works with the "moov atom" at the start of the file.
- Carries subtitles, chapters, multiple audio tracks, and embedded metadata.
- ISO-standardized (ISO/IEC 14496-14) and patent-licensable via MPEG LA.
Limitations
- Codec licensing (H.264, H.265) carries royalty costs for commercial use.
- Streaming requires the moov atom at the start — a misplaced atom breaks web playback.
- Not ideal for lossless or professional editing workflows (use ProRes or DNxHD instead).
FLV Strengths
- Low overhead — the container is extremely compact.
- Designed for streaming — progressive download and seeking work well.
- Decoded natively by Flash Player on every OS for 20 years.
Limitations
- Flash Player is dead — no modern browser can play FLV without conversion.
- Legacy codecs (Sorenson, VP6) are poorly supported in modern tooling.
- Hardware video decoders never added FLV support.
Quality & Compatibility
FLV is a container, not a codec. It can carry H.264 (AVC) video and either MP3 or AAC audio, the same codecs most MP4 files already use. When those codecs are preserved, video quality is lossless at the encoding level — no re-encode means no generation loss. However, FLV does not support HDR metadata (no BT.2020 or PQ/HLG transfer curves), wide-color primaries are carried through but ignored by virtually all FLV decoders, and any embedded subtitle tracks, chapter markers, or cover-art metadata present in MP4 are dropped. Alpha-channel video (MP4 with HEVC or VP9 transparency) cannot be represented in FLV. Audio beyond stereo (5.1 or 7.1) is not supported in FLV's AAC profile as used by most decoders. If the source MP4 uses HEVC (H.265) or AV1, those codecs are incompatible with the FLV container and the video must be transcoded to H.264, which does introduce lossy recompression and quality depends entirely on the chosen bitrate.
Tips for Best Results
- If your MP4 uses H.264 video and AAC or MP3 audio, the conversion can remux without re-encoding — verify by checking the source codec in a tool like MediaInfo before uploading, since remux preserves exact quality while transcode does not.
- FLV caps practical resolution at 1080p for most legacy Flash players; files above that resolution will remux but may fail to play back in the target environment — downscale to 1080p or 720p if the destination player is known to choke on higher resolutions.
- If the target system is an RTMP server, confirm whether it expects FLV with the legacy audio codec Sorenson Spark (which requires full transcoding from H.264) versus FLV with H.264 — newer Wowza and AMS releases accept H.264-in-FLV directly, saving a quality-loss transcode step.
Frequently Asked Questions
Only when it has to. If the codecs inside MP4 (usually H.264 or H.265 for video, AAC for audio) are accepted by FLV, we stream-copy — the bytes are repackaged into the new container with zero re-encoding and no quality loss. When the source uses a codec the target does not support, we transcode at a matching bitrate to keep the visual quality close to the original.
With stream copy, expect the job to finish in seconds to tens of seconds regardless of video length — the work is mostly rewriting the container. Transcoding is slower (roughly real-time: a ten-minute clip takes about ten minutes) because every frame must be decoded and re-encoded. The progress bar shows which mode applies.
Yes. Resolution, frame rate, colour space and bit depth are preserved by default; stream copy is literally bit-identical on these parameters. If you explicitly pick a lower bitrate or a different codec in Advanced, the output is rebuilt to those settings, but the default is always "match the source".
MP4 Video
Source formatMP4 is the most universally supported video container format. It typically uses H.264 or H.265 video codecs with AAC audio, providing an excellent balance of quality and file size across all devices and platforms.
Flash Video
Target formatFLV was the dominant web video format during the Flash era. While Flash is now deprecated, many legacy video files still exist in FLV format and need conversion to modern formats.
Going the other way? Convert FLV back to MP4 with the same engine.
Common Use Cases
Share across platforms
Send FLV files to anyone without worrying about whether they have the right software for MP4.
Embed in documents
Drop FLV output into Word, Google Docs, PowerPoint, Notion or a website without conversion warnings.
Optimize size
FLV often produces smaller files than MP4 for web, email and storage.
Archive & future-proof
Store in a widely-supported format that will still open on future operating systems without legacy plugins.
MP4 vs FLV — Typical file sizes
Approximate file sizes for common scenarios.
- Smartphone video (1080p, 1 min) 60–120 MB
- 4K video (1 min, H.265) 200–400 MB
- Streamed movie (90 min, H.264) 1–4 GB
- 10-min YouTube 2008-era video 40-80 MB
- 45-min TV show (FLV H.264) 200-500 MB
Working with 4K/8K Video or Files Over 100MB?
Web browsers impose strict RAM limits on media streams. For gigabyte 4K/8K footage, GPU-accelerated NVENC transcode, or batch subtitle muxing, dedicated desktop encoders deliver zero upload delays.
One-time payment with zero recurring commitment: convert files up to 1 GB, OCR, PDF/A, and .ZIP batches for 24 hours.
Full 7 days of unlimited conversions, up to 2 GB per file, 100% ad-free with zero subscription.
High-throughput enterprise pipeline for files up to 2,048 MB, 50-file batches, ISO PDF/A, and priority processing.
Uncapped 4K/8K multi-track transcoding with hardware NVENC, VideoToolbox, and AV1/HEVC pipelines.
10-bit color grading workflows, Apple ProRes mastering, and automated watch-folder queues.
Related comparisons
See these formats side by side to understand which fits your use case best.
Related Guides
MP4 Container Format: The Universal Video Standard
Deep dive into MP4 container format: ISOBMFF box structure, fMP4 streaming, fast-start optimization, codec compatibility, and ffmpeg encoding commands.
Read guide →MP4: The Universal Video Container — Technical Deep Dive
Complete MP4 guide: ISOBMFF box architecture (ftyp/moov/mdat/stbl), moov-at-front fast start optimization, fragmented MP4 for DASH/HLS streaming, H.264 vs...
Read guide →AAC: Advanced Audio Coding — The Format Behind Every MP4 and iPhone
Complete AAC guide: LC, HE-AAC v1/v2, AAC-ELD profiles, M4A vs ADTS containers, FFmpeg libfdk_aac encoding, VBR modes, Python Pydub and Mutagen metadata...
Read guide →
</>
Embed this tool on your website or blog (Free)
▼
Add this converter to your site in 10 seconds
Help your visitors convert files directly from your documentation, CMS, or blog. Copy the lightweight HTML snippet below — zero dependencies, responsive, and 100% free.
Secure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.