FLV to AVCHD Converter

Converting FLV to AVCHD: What to Expect

AVCHD is the camcorder format Sony and Panasonic introduced jointly in 2006 for consumer HD recording: H.264/AVC video and Dolby AC-3 audio multiplexed into an MPEG transport stream. FLV is the opposite kind of thing — Adobe's Flash Video container, usually holding low-resolution web video encoded with Sorenson Spark or VP6, sometimes H.264 in later files, with MP3 or AAC audio. This walk-through covers what happens when you push one into the other, which settings are locked and why, what the downloaded file actually is, and the point at which this conversion stops being the right answer.

How to Convert FLV to AVCHD

1. Upload Your FLV File: Drag and drop the .flv onto the page or click "Add Files" to browse. Several files can be queued and converted with the same settings, each uploaded over an encrypted connection.
2. Leave the Codecs Alone: Video Codec is fixed to H.264 and Audio Codec to AC3 — those are the only entries in either list on this page, because they are what the AVCHD specification permits. There is nothing to change and nothing to get wrong.
3. Choose a Resolution and Compression Mode (Optional): Video resolution starts on Keep original; Preset Resolutions offers 720p and 1080p among others if you genuinely need an HD frame. File Compression starts on Quality Preset at "Very High (Recommended)", with Specific file size, Constant Bitrate, Variable Bitrate, Constant Quality and Constraint Quality as alternatives. Trim takes a Start time and Duration in seconds or as HH:MM:SS.sss.
4. Convert and Download: Click Convert and take the file. Files are processed on our servers and deleted automatically after a few hours. No sign-up, no watermark.

Walk-through: What You Actually Get

The download is named with an .avchd extension, and that is worth explaining, because AVCHD is a specification rather than a file type — real AVCHD recordings are named .mts or .m2ts. Inside the file is an MPEG transport stream carrying an H.264 video track and an AC-3 audio track, which is exactly the AVCHD stream format. The practical implication is about file associations, not about the data:

• VLC, mpv, MPC-HC and ffmpeg-based tools identify the stream by inspecting it, so they open the file as it comes.
• Camcorder software, Blu-ray authoring tools and most consumer players route on the extension. Rename movie.avchd to movie.mts (or .m2ts) and they will pick it up. No re-conversion is needed — the bytes are already correct.
• If you would rather not rename anything, FLV to MTS writes the same kind of transport stream with the conventional extension already on it. Note that the MTS and M2TS pages default to AAC audio, so if AC-3 is what you need, either switch the Audio Codec there or use this page and rename.

The second thing to be clear-eyed about is resolution. Most FLV files are modest web-resolution video — 320x240, 480x360, or at best 720p in later H.264 files — while AVCHD's entire purpose is HD. You can fit a small FLV into AVCHD, but upscaling a 480p clip to 1080p only stretches the pixels it already has. It buys container compatibility, not detail.

AVCHD at a Glance

The Three Transport-Stream Targets Compared

Common Errors and How to Fix Them

• "Nothing on my computer will open the file." The .avchd extension has no file association anywhere. Rename it to .mts or .m2ts, or open it in VLC, which ignores the extension entirely.
• "My Blu-ray player or camcorder software rejects it." Two usual causes: the extension (rename it) or the fact that a loose stream is not a disc. Authoring software has to write the BDMV and STREAM folder structure before a player will treat it as AVCHD media.
• "The picture looks soft or blocky after I chose 1080p." A web-resolution FLV has no HD detail to recover. Upscaling stretches the pixels it already has. Keep the resolution at or near the source size and spend the bits on quality instead.
• "The file is enormous." A transport stream carries no compression advantage of its own, and "Very High" is a generous preset for a small source. Switch File Compression to Constant Bitrate and pick something inside the AVCHD envelope, or use Specific file size.
• "Audio and video drift apart." Old Flash recordings sometimes carry irregular frame timing or broken timestamps from streaming. Setting an explicit resolution preset and a constant bitrate makes the encoder re-time the output cleanly.

When This Doesn't Work

AVCHD is a rigid specification: defined resolution tiers, defined H.264 levels, and a 24 Mbit/s ceiling (28 Mbit/s under the 2011 AVCHD Progressive amendment). A non-conforming source has to be constrained to fit, which is why some clips are downscaled or capped. Just as important, this converter produces the H.264 + AC-3 stream — it does not burn a playable disc. To make an AVCHD disc or card that a standalone player or camcorder will mount, drop the converted file into AVCHD authoring software such as multiAVCHD or tsMuxeR, which generates the BDMV index files around your stream. And if you only need the clip to play somewhere, remember that the FLV container itself still opens fine in VLC and ffmpeg — you may not need AVCHD at all. For a universally playable file, FLV to MP4 is almost always the better target.

Frequently Asked Questions

Why does the file have an .avchd extension instead of .mts or .m2ts?

Because AVCHD is a specification, not a true file extension — camcorders write .mts, and computers use .m2ts once a clip has been imported into a BDMV folder. The .avchd file you download holds the same H.264-in-transport-stream bytes; the extension is only a label your workflow may or may not accept. If a tool insists on a different extension, rename the file. Nothing about the payload changes, and no re-conversion is needed.

Why can I not choose AAC or any other audio codec here?

Because AVCHD does not allow it. We checked the option lists on this page: Video Codec contains H.264 alone and Audio Codec contains AC3 alone. The specification permits Dolby Digital AC-3 or uncompressed linear PCM and nothing else, so the page offers AC3 only rather than letting you build a file that calls itself AVCHD and then gets rejected by the first hardware player that reads it. If you want AAC in a transport stream — perfectly reasonable when the destination is a computer or a media server — use FLV to MTS instead, where AAC is the default.

Will converting a low-resolution FLV to AVCHD make it high definition?

No. AVCHD is a high-definition format, but it cannot invent detail that was never recorded. Most Flash-era video is 480p or smaller; selecting 1080p under Preset Resolutions stretches those pixels across a bigger frame and produces a soft, upscaled image in a much larger file. The output is genuinely HD only if the FLV source was already HD, which is unusual for the format. Stepping up only as far as 720p is the gentler compromise.

Is the file I download a finished AVCHD disc or memory card?

No. What you get is the AVCHD video stream. A player-ready AVCHD disc or card also needs the BDMV directory structure, the STREAM folder, the clip-information and playlist files, and the index metadata — all of which authoring software writes. This file is the correct input to that authoring step, not a substitute for it. Copying it loose onto an SD card will not make a camcorder recognise it.

Why does my FLV audio get re-encoded when I convert to AVCHD?

Because FLV and AVCHD use different audio codecs. FLV typically carries MP3, AAC or ADPCM audio, while AVCHD requires AC-3 or linear PCM. There is no way to keep the original track inside an AVCHD-compliant stream, so the audio is always re-encoded to AC-3. The video is re-encoded too — even an FLV that already contains H.264 is decoded and compressed again rather than copied through.

What bitrate keeps the file inside the AVCHD envelope?

AVCHD caps at 24 Mbit/s, dropping to 18 Mbit/s for material recorded to DVD media, and the 2011 AVCHD Progressive amendment raised the ceiling to 28 Mbit/s for 1080/50p and 1080/60p. Switch File Compression to Constant Bitrate and stay under whichever of those applies to your target device. For a web-resolution FLV source, anything above roughly 8 Mbit/s is spending bits on compression artefacts the source already had.

Can I convert just one section of a long Flash recording?

Yes. Switch Trim from Unchanged to Time Range and enter a Start time and a Duration, either in plain seconds or as HH:MM:SS.sss. Only that window is decoded and re-encoded, so it is also the fastest way to test your resolution and bitrate choices before committing to a full-length file.

Should I convert my FLV to MP4 instead?

For nearly everything except a camcorder or AVCHD-disc workflow, yes. MP4 plays on phones, browsers, smart TVs, editors and media servers with no folder structure, no authoring step and no renaming — use FLV to MP4. Pick AVCHD only when a specific device or authoring tool genuinely requires an H.264 transport stream with AC-3 audio. To go the other direction and pull AVCHD footage back into a Flash-era container, see AVCHD to FLV.