So You Found Coolmatn and Now You Want to Use It
I stumbled across Coolmatn about two years ago when someone linked to it in a thread about batch processing images. Nobody could explain it clearly, so I downloaded it and spent three days figuring out how it actually works. Here's what I learned. Coolmatn is a command-line utility for automating media file conversions and metadata stripping. It's not a full production suite. It won't replace FFmpeg or your batch tools, but it fills a specific gap for people who need to mass-process files without writing custom scripts. The interface is minimal. You point it at a folder, set your parameters, and it runs. That's the entire value proposition. It handles encoding presets, EXIF removal, thumbnail generation, and basic file renaming in one pass.
I use it mainly for cleaning up raw footage before handing it off to a client who only accepts H.264 MP4s with no metadata attached. It takes about four seconds per file on my machine. A two-hour job now takes roughly twelve minutes, including the thumbnail pass.
Installation
The latest build is available from the official repository. Grab the binary for your OS, extract it somewhere in your PATH, and run it once to generate the config file. The config sits at ~/.coolmatn/config.yaml on Linux and macOS. Windows users will find it in %APPDATA%\coolmatn\config.yaml. You'll need FFmpeg installed separately. Coolmatn wraps it rather than bundling it, which means you get FFmpeg updates independently. If your FFmpeg version is older than 5.0, some of the newer color space flags will fail silently. I learned this the hard way.
First Run Walkthrough
After installing, open the config file and adjust the defaults. The preset that ships with it is conservative. It outputs at medium bitrate with no metadata stripping. You probably want to change that. Here's a typical setup I use: Create a folder called "working" and drop your source files in there. Then run:
coolmatn process --input ./working --output ./finished --preset clean --strip-meta --generate-thumbs That single line will convert every supported file in the input folder to H.264, remove all embedded metadata, and spit out thumbnails alongside each output file. It runs them sequentially by default. If you want parallel processing, add --threads equal to your core count. Going above 8 threads on my system causes memory spikes because of how FFmpeg allocates buffers internally. I keep it at 6 and everything stays stable.
A Problem I Ran Into
Last year I tried using Coolmatn on a batch of 4K ProRes files. The first twenty processed fine. Then it started throwing allocation errors around file thirty-seven. I spent an hour digging through the logs before I realized the issue wasn't Coolmatn itself. It was the temp directory. The tool writes intermediate files to /tmp on Unix systems, and my /tmp partition was mounted with the noexec flag for security. The fix was pointing the temp directory to a regular partition with this flag in the config: temp_dir: /home/username/temp_processing Once I did that, the batch finished without a single error. I wish the error message had been more descriptive. It just said "IO Error" which is not helpful when you're dealing with fifty files and no sleep.
Things Coolmatn Won't Do Well
It doesn't handle color grading. If your source files need lumetri adjustments or LUT application, you'll need to do that separately. Coolmatn passes through whatever color space you tell it to, which is useful if you know what you're doing and dangerous if you don't. It also doesn't validate output files after encoding. There's no post-pass checksum or playback verification. I once delivered a batch where roughly five percent of the files had corrupted audio tracks because the source material had embedded dropout issues that Coolmatn copied straight through. The fix was running a separate audio validation step. I use ffprobe for this: ffprobe -v error -select_streams a -show_entries stream=codec_name,sample_rate -of csv=p=0 output.mp4
If that returns something other than pcm_s16le or aac with a sane sample rate, the file is bad and needs re-processing.
When You Should Skip Coolmatn
If you need to process fewer than ten files, just use FFmpeg directly. The overhead of setting up a Coolmatn config isn't worth it for small batches. If you need granular control over CRF values, custom bitstream filters, or frame-level scripting, look at something like HandBrakeCLI or write your own Python script with MoviePy. Coolmatn is for people who want a middle ground between a GUI app and raw FFmpeg commands. It also doesn't have GPU acceleration built in. It relies on whatever hardware encoding options your FFmpeg build supports. Check your FFmpeg configuration with ffmpeg -hwaccels before assuming it'll use your GPU. Some distro builds compile without VA-API or NVENC support by default. The project hasn't had a major update in about fourteen months. Features are stable but new ones aren't coming fast. If you're okay with a tool that does what it says without constant changes, it's solid. If you want cutting-edge format support, you'll be waiting.
Bottom Line
Coolmatn is a practical tool for a narrow use case. It won't impress anyone at a conference. It will save you time on repetitive conversion tasks where you don't need fancy features, just consistent results. Install it, read the config file carefully, point it at a folder, and let it run. If something breaks, check your temp directory and your FFmpeg version first. Those two things cause eighty percent of the issues I've seen.
