Jpegfinder

What?

Jpegfinder is a tiny tool for scraping through files (or block devices) and finding and extracting anything which looks a bit like a JPEG image.

Why?

I have a Hubsan H107D drone, which records video onto an SD card; but it's buggy and the resulting AVI MJPEG files are hopelessly corrupt. Jpegfinder will extract any (surviving) frames of video from the files, and then I can turn them into playable videos.

It's also useful for extracting interesting looking jpegs from any binary file. I suppose technically it's a forensics tool.

How?

Compile the tool (by running make). Invoke with:

$ jpegfinder -f broken.avi -j outputdir -w 720 -h 240

Command line flags are:

• -f filename.avi: specifies the input file.

• -j outputdir: specifies the directory output files go.

• -w width -h height: if set to anything other than 0, then only jpegs of this size will be output. This is useful for reducing false positives when you know the size of the images you're looking for (like I do for my videos). (If not set, jpegfinder will emit everything, including garbage.)

• -o offset: start looking at this offset. Useful for resuming a scan (because scans are slow).

Output files are named by the hex offset into the source file. This is so each file has a stable name, allowing runs to be repeated or resumed and you get the same names each time.

You can create a non-corrupt MJPEG video containing the output frames using ffmpeg, like this:

$ ffmpeg -f image2 -pattern_type glob -framerate 60 -i 'jpegs/*.jpg' -vcodec copy output.mkv

Note that if jpegfinder found any false positives, you'll get corrupt frames. But any competent video editor should find and ignore them. At least the file will be loadable (unlike the source).

Who?

jpegfinder was written entirely by me, David Given. Feel free to send me email at [email protected]. You may also like to visit my website; there may or may not be something interesting there.

License?

jpefinder is open source software available under the 2-clause BSD license. Simplified summary: do what you like with it, just don't claim you wrote it.