1

This is the best my actioncam can create.

Rollei Wifi 5S

My goal is to take advantage of this low quality and save as much harddrive space as possible so visible quality remains.

Which measurements can I take using which windows programs to exploit the already low quality and save as much space as possible?

3

There are a few video quality metrics available for you to use, primarily SSIM and also PSNR. You can use ffmpeg to convert the video and then compare the output.

Step 1 Convert the video

ffmpeg -i actioncamfile -c:v libx264 -crf 23 -c:a copy -map 0 compressed.mp4

The CRF value modulates the quality. Lower values produce better quality but larger file sizes. Typical values range from 18 to 28, but absolute range is 0 to 51, but 0 being lossless, which will produce an exact looking file but will be bloated.

If you want to test with only a small section, say 20 seconds of the source starting from 15 seconds into the file, you can use

ffmpeg -ss 15 -i actioncamfile -t 20 -c:v libx264 -crf 23 -c:a copy -map 0 compressed.mp4

Step 2 Measure the quality of the conversion

Run

ffmpeg -i compressed.mp4 -i actioncamfile -lavfi "ssim;[0:v][1:v]psnr" -f null -

This command output, at its end, will display lines like this

[Parsed_ssim_0 @ 000000000039ad80] SSIM Y:0.984483 U:0.980458 V:0.980921 All:0.983219 (17.751712)
[Parsed_psnr_1 @ 0000000000398320] PSNR y:42.63 u:43.19 v:44.09 average:42.90 min:42.07 max:46.16

You can aim for a SSIM All value to be at least 0.99, or set your own benchmark, based on what's acceptable.

| improve this answer | |
  • For some reason, All: stays at 0.7 no matter what crf is like between 18 and 37. My commands: pastebin.com/asQrmmq0 – Vitalis Hommel Feb 10 '16 at 13:51
  • Try without -ss – Gyan Feb 10 '16 at 13:54

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