Testing CompressO – Lossless compression results (630 MB → 1.14 GB?)

[darkpsinight]

I tested CompressO (downloaded from GitHub) using the Lossless Compression setting.

• Input video size: 630 MB
• Output video size after lossless compression: 1.14 GB
• Instead of compressing the file, the software produced a significantly larger output.

I understand that lossless video compression can sometimes result in larger files depending on the source codec and content, but a nearly 2× size increase was unexpected !!!

Test details:

• Output format: MP4
• Settings used: as shown in the attached screenshot (Lossless Compression, default Codec, Dimensions, FPS, etc.)

Has anyone else experienced this? Is this expected behavior for certain types of source videos, or could there be a configuration issue?
Open to suggestions or explanations.

Attached: screenshot of CompressO interface with input/output sizes.

[iuvi7]

DecompressO 😆

[niraj-khatiwada]

That is expected behavior from FFmpeg. Lossless compression almost always produces larger output size than original, especially for media files that were already lossy in the first place.

[darkpsinight]

Then what is the solution for compressing this video correctly, achieving the lowest quality loss and the biggest size reduction?

[niraj-khatiwada]

So, changing the quality of the video implies lossy compression. For lowest possible quality, turn off "Lossless Comprsssion" and set quality to "Low". If can even reduce the size if you resize the video to lower resolution using "Dimensions" setting. If you want optimal size video with minimal quality difference, you can set the quality to "Medium"(50%), which is default settings.