MJPEG to WTV Converter

MJPEG to WTV — the Page Where the Codec Is Chosen For You

.wtv is Windows Recorded TV Show, the container Windows Media Center writes when it records television. Microsoft's own documentation describes the plumbing: the Stream Buffer Engine writes recordings to \Users\public\Recorded TV\ with a .wtv extension, it handles MPEG-2 video with MPEG-1 Layer II or Dolby Digital AC-3 audio at capture rates up to 30 Mbit/s, and it replaced the older .dvr-ms format in Windows 7.

Motion JPEG is the opposite kind of file: video as a run of complete, independent JPEG frames, with no compression between them, which is why IP cameras and machine-vision systems produce it and why the files are so large. Converting one into the other is a legitimate job — putting camera footage into a Media Center library, say — and this page does it. What makes the page unusual is the control surface.

Two Dropdowns With Nothing In Them

Open Advanced Options and you will find a Video Codec group and an Audio Codec group that both render with no selectable entries. That is not a loading failure and it is not a page that forgot to populate — the choice is simply fixed for WTV output, and the groups appear because they are shared across every video target on the site.

Fixed to what is the useful question, and we measured it rather than guessing:

This is worth stating plainly because it is easy to assume otherwise. Left entirely to itself, the WTV muxer's own preference is MPEG-2 video — we confirmed that a conversion with no codec specified transcodes H.264 down to mpeg2video. The pipeline overrides that and asks for H.264, so what you get is a WTV container carrying modern video, which is a different thing from what a Media Center tuner would have written into the same container.

How to Convert MJPEG to WTV

1. Upload Your MJPEG File: Drag the .mjpeg onto the page or click "+ Add Files". IP-camera exports, webcam captures and old camcorder clips all work, and several can be queued with the same settings.
2. Choose a File Compression Mode: The mode is preselected to Quality Preset. Constant Quality exposes a CRF slider running 16 to 51 and opening at 23, where lower means better quality and a larger file. Specific file size, Constant Bitrate, Variable Bitrate and Constraint Quality are the other four modes.
3. Set Video Resolution: Preselected to Keep original, which is what you want for camera and evidence footage. Percentage, preset heights, an explicit width, an explicit height and a full width × height are all available beside it.
4. Trim and Convert: If you use Trim, leave the start time at 0 — the reason is in the next section. Click "Convert" and save the .wtv. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark.

How Our WTV Compares to a Media Center Recording

Common Errors and How to Fix Them

• "The output is empty or a couple of hundred bytes." You set a Trim start time above zero. A raw Motion JPEG stream carries no timestamps, so there is nothing to seek against and the encoder receives no frames. We measured a trim starting at 2 seconds producing a container with zero frames, and a start of 0.04 seconds — one frame at 25 fps — doing exactly the same. A start of 0 with a duration set works normally and produced exactly 2.000 seconds.
• "The clip is silent." A raw Motion JPEG stream has no audio track, because the format provides nowhere to store one. Nothing can be carried across. Sources that are really AVI, MOV or MKV under an .mjpeg name do have audio and will get the AC-3 track described above.
• "The file is bigger than I expected for the length." WTV carries meaningful per-packet overhead. On a six-second conversion the encoder reported 717 KiB of video payload inside a 782,336-byte file — about 6.6% spent on container structure. That is normal for the format.
• "The playback speed is wrong." A raw Motion JPEG stream stores no frame rate, so a nominal 25 fps is assumed. Footage shot at 15 or 30 will play fast or slow. Converting from the original container instead fixes this.
• "Windows will not open it." Windows Media Center was the application built for this format, and it has not shipped in a consumer Windows release for years. VLC and ffmpeg-based tools read WTV; the modern Windows video player generally does not.

When This Doesn't Work

The most common disappointment with this conversion is not technical, it is expectational: a WTV file produced here is a valid WTV container, but it is not a Media Center recording. Real recordings come out of the Stream Buffer Engine with their elementary streams encrypted, and Microsoft's documentation is explicit that access depends on the broadcaster's copy-protection flag — where the flag is set, playback is restricted to the PC that made the recording. Nothing produced by a converter carries that machinery, and nothing produced by a converter can remove it from a file that has it.

The other case is simpler. If nothing in your workflow named .wtv, do not use it. The format's software ecosystem has been shrinking since Media Center was discontinued, and you gain nothing from the container. MJPEG to MP4 gives you the same H.264 video, far better compatibility and a much smaller file; MJPEG to AVI is the choice if a legacy Windows tool needs something older.

Frequently Asked Questions

Why are the Video Codec and Audio Codec dropdowns empty?

Because the codecs are fixed for this target, and the groups are shared components that render regardless. The practical effect is that you cannot change them — and you do not need to, because the values chosen are already the sensible ones. We verified the result directly: H.264 video and AC-3 audio at 48 kHz.

Is the output MPEG-2 like a real Media Center recording?

No, and this is the one place where our output diverges from what Media Center would write. Microsoft's documentation says the Stream Buffer Engine handles MPEG-2 video with MPEG-1 Layer II or AC-3 audio. This conversion writes H.264 into the same container instead. The audio side matches — AC-3 is one of the two the SBE uses — but the video does not.

Will Windows Media Center play the file I get?

There is no way to promise that. Media Center expects the video profile its own tuner produced, and it has not shipped in a consumer Windows release for a long time. If a specific Media Center installation is your target, test with a short clip before converting a library.

How much smaller will the WTV be than the MJPEG?

Considerably, because almost anything beats storing every frame as a full JPEG. Our six-second 640 × 480 sample went from 3,575,215 bytes of Motion JPEG to 782,336 bytes of WTV at the default quality — a little over a fifth, and that is with 6.6% of the output spent on container overhead.

Where should I put the Constant Quality slider?

It runs 16 to 51 and opens at 23, which is a good general-purpose setting. Around 18 is effectively indistinguishable from the source on typical camera footage; 28 makes a noticeably smaller review copy; above 35 the artefacts become obvious. Remember that lower numbers mean better quality here, which is the opposite of how a percentage-style quality control behaves.

Can I convert a WTV recording the other way and get my TV show as MP4?

Only if the recording is not copy-protected. Media Center encrypted the elementary streams it wrote, and where the broadcaster set the CGMS-A copy-protection flag, playback is tied to the recording PC. An unprotected recording converts like any other video; a protected one cannot be decoded by anything other than the machine that made it.

Should I keep the original resolution?

For camera, evidence and scientific footage, yes — Keep original is preselected for that reason, and rescaling introduces resampling you probably do not want in the record. For review copies, halving the height roughly quarters the pixel count and the file size with it.

Does the conversion re-encode or re-wrap?

It re-encodes. Motion JPEG and H.264 are entirely different coding schemes, so every frame is decoded and recompressed — which is exactly where the size reduction comes from. Keep the original if the footage is evidential, since the output is one generation removed from it.

Why does the file size overhead matter here more than in MP4?

Because WTV is a recording format, not a delivery format: it was designed around live streams that can be paused, seeked and resumed, and that machinery costs structure on disk. Around 6.6% on our test conversion is typical. MP4 spends far less, which is one more reason to prefer it unless the extension itself is the requirement.