Why Are eos-movrec Files So Big? MJPEG File Size Explained
You recorded eleven seconds of video and got a 41 MB file. Nothing is broken — that is simply what happens when software from 2010 saves video the simple way. EOS Camera Movie Record stores every single frame as its own JPEG photo, one after another, with no compression between frames. This page does the bitrate math, explains why the software works this way, and shows what to do when the files get unwieldy.
Quick answer
eos-movrec files are huge because they use MJPEG (Motion JPEG): each frame is compressed on its own like a still photo, but nothing is ever shared between frames. Modern codecs like H.264 store only the changes from frame to frame, which is why the same 11 seconds shrinks to roughly a tenth of the size after conversion. The big files are normal, expected, and fixable.
The math: where 41 MB comes from
Take the 450D: each frame is 848 × 560 pixels = 474,880 pixels. Uncompressed, at 3 bytes per pixel, that is about 1.4 MB per frame. At roughly 22 frames per second, raw video would be around 30 MB every second — utterly unmanageable.
MJPEG compresses each frame roughly the way a JPEG photo is compressed — typically around 10:1. So 30 MB/s of raw frames becomes roughly 3 MB/s, or about 180 MB per minute. The observed real-world figure matches: 41 MB for 11 seconds is ~3.7 MB/s, right in that range (that particular measurement came from a 40D at 1024×640 — bigger frames, slightly bigger files).
| Camera | Frame size | Rough MJPEG bitrate | Per minute |
|---|---|---|---|
| 1000D / Rebel XS | 768 × 512 | ~2.5 MB/s | ~150 MB |
| 450D / Rebel XSi | 848 × 560 | ~3 MB/s | ~180 MB |
| 40D / 50D | 1024 × 680 | ~3.7 MB/s | ~220 MB |
These are approximations — the exact size depends on scene complexity (a busy scene compresses worse than a plain wall) — but they explain the order of magnitude. Compare: the same footage as H.264 at good quality runs about 3 Mbps — roughly ten times smaller.
MJPEG vs. H.264: the one-paragraph version
MJPEG treats video as a flipbook of independent JPEG photos. That is simple and robust — any frame can be decoded alone, which is why scrubbing MJPEG is instant — but wasteful, because nearly identical consecutive frames are stored in full every time. H.264 instead stores one full frame and then only the differences for the following frames. In a typical talking-head shot, most of the picture barely changes between frames, so “just the differences” is enormously smaller. The price is complexity: H.264 needs far more processing power to encode, which is exactly why a 2010-era USB capture tool did not use it.
Why eos-movrec uses MJPEG in the first place
It was a deliberate engineering trade-off, not laziness. eos-movrec grabs Live View frames over USB 2.0 in real time on whatever PC you have — including weak 2010-era laptops. MJPEG encoding is cheap: compress one frame, write it, forget it, repeat. H.264 would have required analyzing motion across frames live, which those machines could not do reliably at 22 fps. MJPEG also degrades gracefully: if the USB bus hiccups and a frame arrives late, you lose one frame, not a whole group of dependent frames. For a free tool capturing video through a protocol never designed for video, MJPEG was the sane choice — and the giant files are its known cost.
Can eos-movrec record smaller files directly?
No — there is no quality or codec setting that changes this; MJPEG AVI is simply what the software writes. The intended workflow is record big, compress after. That is also why the files land on your computer’s hard drive, not the camera’s memory card: the PC does the capturing, so a bigger card in the camera changes nothing. If disk space during long sessions worries you, record to a drive with plenty of free space (or an external SSD via our storage picks) and compress afterwards.
Files too big? Shrink them here
The fix takes minutes and is nearly lossless at the right settings. Two guides, pick your style:
- Command line: Convert eos-movrec AVI to MP4 with FFmpeg — one command, plus a batch script that converts a whole folder while you do something else.
- Point and click: Compress MJPEG files with HandBrake — preset walkthrough with H.264, CRF 20–23, and your native resolution preserved.
Either way, expect roughly a 10× reduction: that 41 MB clip becomes about 4 MB, ready to upload or archive. And once the files are small, the rest of the pipeline opens up — editing in DaVinci Resolve, or even upscaling for free.
Frequently asked questions
Is 41 MB for 11 seconds of video normal?
Yes — completely normal for eos-movrec. That figure (~3.7 MB/s) lines up exactly with MJPEG math for a 1024×640-class frame at ~20 fps. Smaller bodies record slightly smaller files (a 1000D at 768×512 runs about 2.5 MB/s), but the order of magnitude is the same. It is not a bug, a wrong setting, or a failing cable.
Will a bigger memory card in my camera help?
No. eos-movrec captures Live View frames over USB and writes the AVI to your computer’s hard drive — the camera’s memory card is not involved at all. If you are running out of space during long sessions, free up room on the PC’s drive (or record to an external drive) instead.
Does a higher-resolution camera model make bigger files?
Yes, proportionally. MJPEG size scales with pixel count: a 40D/50D at 1024×680 produces noticeably larger files than a 1000D at 768×512 recording the same scene for the same duration. Frame rate matters too — anything that pushes the capture toward the ~22 fps ceiling adds frames, and therefore megabytes, per second.
Why is there no audio track making the file even bigger?
Because eos-movrec records video only — there is no audio track by design, and bodies like the 450D/1000D have no microphone input to feed one anyway. Audio at typical bitrates would add only ~1 MB per minute, so its absence barely dents the file size; the video frames are the whole story. See our no-audio guide for the sound workaround.
Can I make eos-movrec record straight to MP4?
No — MJPEG AVI is the software’s only output format, with no codec or quality settings to change. The intended workflow is record-then-convert: capture the big AVI, then run it through FFmpeg or HandBrake for a ~10× smaller H.264 MP4 at visually identical quality.
Is MJPEG lower quality than H.264, since the files are so simple?
Counterintuitively, per-frame MJPEG quality is quite high — every frame is a complete, independently compressed image with no temporal artifacts or motion-prediction errors. That is why the AVIs make fine archival masters. H.264 at CRF 20 keeps essentially all of that visible quality while deleting the massive redundancy between frames. Big does not mean better here; it just means uncompressed-between-frames.