CAVS to FLV Converter

Convert CAVS to FLV: What This Tutorial Covers

This walk-through is for anyone holding a raw .cavs file — a Chinese AVS (AVS1) video bitstream that almost nothing plays directly — who needs it wrapped into FLV for a legacy Flash-based player, CMS, or e-learning toolchain that still ingests .flv. Two honest cautions up front: a bare .cavs is video-only, so the FLV comes out silent, and FLV itself is a dead web-delivery format. If your real goal is durable, universal playback, CAVS to MP4 is the better target — convert to FLV only when something downstream genuinely demands that extension.

How to Convert CAVS to FLV

1. Upload Your CAVS File: Drag and drop your .cavs onto the page or click "+ Add Files" to browse from your device. You can queue several raw AVS streams and convert them with the same settings.
2. Pick a Quality Preset: Open Advanced Options and leave "Preset" on "Very High (Recommended)" to stay close to the source, or switch to "Specific file size" to target an exact size in MB. "Constant Bitrate" and "Constant Quality" are there if you need tighter control.
3. Set Resolution or Trim (Optional): Under "Video resolution" choose "Keep original", a "Preset Resolutions" entry, "Resolution Percentage", or an exact "Width x Height". Open "Trim" and switch to "Time Range" to export just one segment from a long capture.
4. Convert and Download: Click "Convert" and download your FLV. No sign-up, no watermark.

Walk-through: Choosing the Right Codec Inside the FLV

The byte that decides how broadly your FLV plays is the video codec, set under "Show All Options". This tool defaults "Video Codec" to FLV — Sorenson Spark, the original H.263-based codec (FourCC FLV1) that every Flash Player from version 6 onward could decode. That is the safest choice for genuinely old players. The audio side stays simple because the source is silent; the converter reserves AAC for any FLV audio track, with MP3 also available, both of which Flash-era players expect.

• If your target is a very old Flash player or courseware that predates 2008 — keep "Video Codec" on FLV (Sorenson Spark). It is the lowest common denominator and will decode anywhere .flv is supported.
• If your downstream tool is newer — Flash Player 9 Update 3 (December 2007) added H.264-in-FLV; switch "Video Codec" to H.264 for noticeably sharper output at the same bitrate, if the receiving system accepts it.
• If file size matters more than fidelity — switch "Preset" to "Specific file size" and let the encoder hit a target in MB rather than chasing maximum quality.

Common Errors and How to Fix Them

• "The FLV has no sound" — Expected, not a bug. A raw .cavs is an AVS1 video elementary stream with no audio to carry, so the output is silent. To get sound you must start from the original container that holds both streams, not the demuxed .cavs.
• "My player won't open the .cavs to preview it first" — Most mainstream players can't decode AVS1-P2. FFmpeg ships an open-source cavs decoder (ffplay file.cavs), which is why a server-side converter is the practical route; once it is FLV, far more tools can read it.
• "No browser will play the finished FLV" — Correct, and unavoidable. No browser plays .flv natively since Flash Player was blocked in January 2021; use VLC, ffmpeg, or MPV to verify the file, or convert to MP4 for browser playback.
• "The picture looks soft or blocky after conversion" — This is second-generation lossy loss (see below). Keep "Preset" on "Very High", leave the native resolution, or switch the codec to H.264-in-FLV so the encoder isn't the bottleneck.
• "Upload of a large broadcast capture stalls" — The realistic limit here is upload time and size, not anything on your device. Use "Trim" → "Time Range" to send only the segment you actually need.

When This Doesn't Work

This conversion can't manufacture quality or sound that the source never had. A .cavs is already lossily coded with AVS1, and FLV holds Sorenson Spark or H.264, so the picture is decoded and re-encoded from scratch — a lossy-to-lossy pass that recovers no detail and keeps standard-definition footage standard-definition. It also can't add an audio track that was never in the elementary stream. And if you uploaded a .avs AviSynth script (a small text frameserving file) by mistake rather than a .cavs AVS1 bitstream, there is no coded picture inside it to wrap. When you simply want footage that plays everywhere with the least fuss, use CAVS to MP4 or the general Video Converter instead of FLV.

Frequently Asked Questions

What exactly is a .cavs file?

It is a raw video elementary stream encoded with AVS1 (Audio Video Coding Standard), China's national video-coding standard, defined by GB/T 20090.2-2006 and promulgated in February 2006 by the AVS Working Group (founded June 2002). The picture uses the AVS1-P2 JiZhun (base) profile, a block-based motion-compensated design broadly comparable to MPEG-2 and H.264. It is most common in Chinese digital-TV and set-top-box environments and rarely seen elsewhere, which is why general-purpose players usually can't open it.

Is FLV dead now that Flash Player is gone?

The web-delivery workflow is dead, but the file format is not unreadable. Adobe ended Flash Player support on December 31, 2020 and began blocking Flash content on January 12, 2021, so no browser plays .flv natively anymore and no modern site serves it. The container itself still opens in VLC, ffmpeg, and MPV-class players, because those decoders never depended on the Flash plug-in. Convert to FLV only when a specific legacy system requires that extension; for anything modern, prefer CAVS to MP4.

Why does the converted FLV have no sound?

Because a raw .cavs file is an AVS1 video elementary stream — picture only, with no audio for the converter to carry. In Chinese AVS workflows the sound was encoded as a separate stream and muxed in only when the final container was built, so the bare .cavs on its own is mute, and the FLV therefore comes out silent. It is not a fault in the conversion — there was never any audio in the source. If you have the original container (an MP4, MKV, or transport stream) that holds both streams, convert that file instead, because the audio lives there.

Which video codec does this output put inside the FLV?

By default, FLV (Sorenson Spark), the original H.263-based codec (FourCC FLV1) that every Flash Player from version 6 onward could decode — the safest choice for old players. If your downstream tool is newer, Flash Player 9 Update 3 (December 2007) added H.264-in-FLV support, so switch "Video Codec" under "Show All Options" to H.264 for better quality at the same bitrate. We don't target On2 VP6 here; Sorenson Spark and H.264 cover the realistic compatibility range.

Will converting CAVS to FLV improve or lose quality?

It will lose a little, and it is one-way. The .cavs stream is already lossily coded with AVS1, and FLV does not carry that codec, so the converter decodes the AVS1 frames and re-encodes them to Sorenson Spark or H.264. That second pass discards some data and no setting brings detail back; a standard-definition source stays standard-definition. Keep "Preset" on "Very High" and leave the native resolution so the re-encode has the most to work with — you can avoid throwing more away, but you can't add any in.

How are my files handled, and how long are they kept?

In our testing, re-encoding a short raw .cavs stream to FLV at the "Very High" preset produced a clean, VLC-playable file with no audio track — exactly what a silent source should yield. Your file is uploaded over an encrypted connection, decoded and re-encoded into FLV on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark, never shared or made public. The realistic limit on very large broadcast captures is upload time, not anything on your device.