FLV Compressor

How to Compress FLV Videos Online

1. Upload Your FLV File: Drag and drop or click "+ Add Files" to select one or more FLV videos. Batch is supported, and processing runs in your browser session — no sign-up, no watermark.
2. Pick a File Compression Method: Choose Quality Preset (Highest to Lowest) for a one-click result, Target file size (%) to shrink by a ratio (e.g., 50% halves the file with Smart Scaling on resolution), Specific file size to hit an exact MB target, Constant Bitrate or Variable Bitrate for manual bitrate control, Constant Quality (CRF slider where lower = better), or Constraint Quality (CRF plus a max bitrate ceiling).
3. Adjust Video Resolution and Trim (Optional): Keep original, scale by percentage, pick a preset (1080p, 720p, 480p, 360p, 240p, 144p), or enter exact width/height. Under Trim, switch from Unchanged to Time Range and set a start point + duration to extract a clip and drop file size further.
4. Compress and Download: Click Compress. Files stay private to your session and download directly to your device.

Why Compress FLV Files?

FLV (Flash Video) was the dominant web video container during the Flash era — introduced in Flash Player 6 in March 2002, used by early YouTube, Hulu, Dailymotion, and Vimeo, and tied to Adobe's Flash Player runtime. Adobe officially discontinued Flash Player on December 31, 2020, and Chrome, Firefox, Edge, and Safari permanently removed Flash support by late January 2021. Yet billions of FLV files still sit in screen-recording archives, e-learning libraries, CCTV exports, and legacy CMS backups. Many were encoded with older codecs (Sorenson Spark, VP6) that are far less efficient than modern H.264 or H.265, so the files are larger than they need to be.

• Archive shrink — Cold-storage video libraries from 2005–2015 are often 2–5x larger than necessary; recompressing with VBR or CRF at the same visual quality typically reclaims 40–70% of disk space.
• Email and chat caps — Gmail rejects attachments over 25 MB and Discord's free tier limits uploads to 10 MB (lowered from 25 MB in September 2024). Targeting an exact MB size moves a 100 MB FLV under those limits in one pass.
• Cheaper cloud storage — S3, Backblaze B2, and Google Drive bill by the gigabyte. Halving a 500 GB FLV archive halves the monthly bill without re-encoding the container.
• Faster legacy uploads — Old learning-management systems (Moodle, Blackboard) and CCTV review portals still accept FLV but throttle large uploads; smaller files clear timeout windows.
• Screen-recording cleanup — Camtasia 7/8, CamStudio, and older OBS builds exported directly to FLV. Trimming dead intro/outro footage plus CRF 23 usually drops these recordings by 60%+.
• Keep the container, drop the bloat — When a downstream tool (an old Flash-based courseware player or legacy editor) still requires .flv specifically, compressing in-place avoids the container change.

FLV vs MP4 vs WebM — Format Comparison

FLV Compression Methods Quick Guide

Frequently Asked Questions

Why is my FLV file so much larger than an equivalent MP4?

Because most FLV files were encoded with Sorenson Spark or VP6, which were state-of-the-art in 2002–2007 but are far less efficient than H.264 (added to FLV in Flash Player 9 Update 3, December 2007) and dramatically less efficient than H.265 or AV1. Re-encoding a Sorenson Spark FLV with modern H.264 inside the same FLV container typically cuts size 40–60% at matched perceptual quality. If you can change container, converting to MP4 usually gives another 5–15% on top.

What's the best compression method for FLV?

For most people: Target file size (%) at 50–60% is the easiest and gives predictable results. For best quality-to-size ratio: Constant Quality with CRF 23 (default) or CRF 26 if you want smaller files. For hitting a hard cap like Gmail's 25 MB or Discord's 10 MB free-tier limit, use Specific file size and enter the exact target. Quality Preset is the fastest if you don't want to think about codec settings.

Can I trim and compress in one pass?

Yes. Set Trim to Time Range, enter a start time and duration, then pick any compression method. The encoder processes only the trimmed segment, so a 20-minute FLV trimmed to a 4-minute highlight starts ~80% smaller before compression even applies.

What CRF value should I use for FLV?

CRF 18 is visually lossless (output indistinguishable from source for most content). CRF 23 is the standard H.264 default — small artifacts under careful inspection, fine for general viewing. CRF 28 is noticeably softer but useful for archival of low-priority footage. Anything above 30 shows blocky compression on fast motion. Each +6 CRF roughly halves the bitrate.

Will compressed FLV files still play in old Flash-based players?

Yes, as long as the codec inside is one the player supports — Sorenson Spark, VP6, or H.264 (Flash Player 9 Update 3 and later). XConvert keeps the FLV container; if you specifically need legacy compatibility, pick H.264 as your codec rather than relying on default settings. Note that no current browser will play any FLV without a third-party plugin, so the only modern playback path is a desktop player like VLC or MPV.

Should I convert FLV to MP4 instead of compressing it as FLV?

If anything downstream still requires the .flv extension (an old Flash-based courseware module, a legacy ingest pipeline), stay in FLV. Otherwise, converting to MP4 is the better long-term move: smaller files at the same quality, universal device support, and HLS/DASH-streamable. For web-only playback, WebM compresses even harder with VP9 or AV1.

How small can I shrink an FLV without it looking bad?

For SD source (480p or below), expect 50–70% reduction at visually transparent quality with H.264 + CRF 22 inside the FLV. For HD source (720p/1080p) originally encoded in VP6, 60–80% reduction is realistic. Beyond that, you start trading visible quality — banding in gradients, blocking on motion. Use the Target file size (%) method and preview at 40% first, then push lower if the result still looks acceptable.

Does compressing already-compressed FLV files lose more quality?

Yes — every lossy re-encode introduces some generational loss because the encoder reads already-quantized frames. To minimize damage: use a higher quality setting than the source (CRF 20 if the source was CRF 23), avoid stacking compress→compress cycles, and keep the original archive copy until you've verified the output. If quality matters and the source is salvageable, re-encode straight from the original master, not the FLV.

Can I compress multiple FLV files at once?

Yes. Upload as many FLV files as you want and the same compression settings apply to all of them in one batch. There's no file count limit and no sign-up required. Each file processes independently, so a one-off bad frame in one video won't stop the rest.