Avisynth MultiThreaded Effects

[lolman]

Does Multithreading in Avisynth can cause quality loosses, or improvements?
Is it difference from filter to filter, function to function?
Is there ways to know quality differences, or measure them?

[jagabo]

No difference in quality. Though there can be issues with out-of-order frames with some source filters. You could use MSU VQM Tool to compare two videos. The usual problems with multithreading are running out of memory and crashing.

[LigH.de]

There are several known multi-threading capable plugins and others which are known to have issues in multi-threaded usage cases because their programming style is not "re-entrant" (cannot easily work in several parallel instances).

AviSynth+ has a per-plugin system to justify the optimal MT mode and maintains an online document as import scriptlet with current recommendations. This may also be a good source to know which plugins to avoid in AviSynth too (functions in MT_SERIALIZED mode will fail when executed multi-threaded, from video corruption to crashes).

[lolman]

Thanks guys.

I do not have MSU VQM Tool.
The free version let not handle 720p

Any other way to calculate quality of 2 or more videos?

[LigH.de]

You can use AviSynth functions Compare for PSNR, or SSIM for SSIM metric, writing out log files which can be analyzed in a spreadsheet calculator (e.g. Excel). Just run an analyzing scipt (comparing two input clips) through AVSMeter once. Important: To actually output the log files, the output video clip of these functions must be part of the final video output of the script (if not, AviSynth may optimize the function call out completely), so if you want to run both Compare and SSIM on the same two input clips, combine both their outputs e.g. using Merge.

c1 = LwLibavVideoSource("clip1")
c2 = LwLibavVideoSource("clip2")
Merge(Compare(c1, c2, "", "compare.log"), SSIM(c1, c2, "ssim.csv", "avgssim.txt", lumimask=true))

The compare.log file may have to be loaded differently into a spreadsheet, I don't know its format right now without trying...

Another free comparison tool is Fritz Framalyzer.

[jagabo]

You can use AviSynth functions Compare for PSNR, or SSIM for SSIM metric

I didn't know AviSynth had that feature. Thanks.

One can also use Subtract(). That shows the difference between the two images. You can follow that with Levels(120,1,135,0,255) to make the differences stand out more. This is a purely visible test. No stats. Or you can follow Subtract() with ColorYUV(analyze=true) to get some numeric stats about the differences.

[SameSelf]

^^Bookmarked! Thanks for sharing.