Kap: Significant slowdown, exporting to disk

[davewhitley]

macOS version: Catalina (10.15)
Kap version: 3.3.2

Steps to reproduce

No plugins installed

• capture a short video
• make sure "export to disk" is selected
• click export
• notice nothing happens, spinning beach ball
• export window remains empty

Current behavior

I can't seem to get the "export to disk" function to work, it just slows down and stalls.

Copy to clipboard is working, MP4 also doesn't work

Expected behavior

To export the gif and not stall.

[marlukcz]

I confirm, the ffmpeg is running in background, but the export process takes much more time than previously. Video length of 30seconds was previously exported in few seconds, now it takes couple of minutes. This make KAP un-usable :-\
Version: Version 3.3.2 (3.3.2.1718)

[carlosbaraza]

Just noticed that the slow export is to AV1. Just export to H264 and it will be as fast as it used to be. It seems to me that the AV1 export is not using the full CPU capabilities, but it somehow limits its resources. Probably the command used to call ffmpeg?

[carlosbaraza]

Could it be related to Hyperkit I/O being slow?

[marlukcz]

OK, when the export is running, there is this process:

/Applications/Kap.app/Contents/Resources/app.asar.unpacked/node_modules/@ffmpeg-installer/darwin-x64/ffmpeg -i /var/folders/_6/mrdyrwds5f58_gjmyj5q6_pn8tl1qv/T/tmp-3634-juBINphQB3aH-.mp4 -r 10 -s 1200x602 -ss 0 -to 39.166667 -c:v libaom-av1 -c:a libopus -crf 34 -b:v 0 -strict experimental -cpu-used 4 -row-mt 1 -tiles 2x2 /private/var/folders/_6/mrdyrwds5f58_gjmyj5q6_pn8tl1qv/T/739ba4bfa1bdac1e86455f6191323d09/Kapture 2020-10-27 at 17.57.46.mp4

This process runs for ~4minutes in this sample.

I copied the raw mp4 file from /var folder to input.mp4 and tried to convert it using different parameters.
Note that in samples bellow, the ffmpeg command is a link to /Applications/Kap.app/Contents/Resources/app.asar.unpacked/node_modules/@ffmpeg-installer/darwin-x64/ffmpeg

1) removed all parameters which I don't understand
time ffmpeg -i input.mp4 -r 10 -s 1200x602 -cpu-used 4 export.mp4
real 0m15.228s
user 0m33.103s
sys 0m0.636s

2) used all specified parameters as KAP application is using:
time ffmpeg -i input.mp4 -r 10 -s 1200x602 -ss 0 -to 39.166667 -c:v libaom-av1 -c:a libopus -crf 34 -b:v 0 -strict experimental -cpu-used 4 -row-mt 1 -tiles 2x2 -cpu-used 4 export.mp4
real 4m4.358s
user 9m22.288s
sys 0m9.574s

3) removed parameter -c:v libaom-av1
time ffmpeg -i input.mp4 -r 10 -s 1200x602 -ss 0 -to 39.166667 -c:a libopus -crf 34 -b:v 0 -strict experimental -cpu-used 4 -row-mt 1 -tiles 2x2 -cpu-used 4 export.mp4
real 0m14.339s
user 0m32.456s
sys 0m0.577s

so the root cause of the problem is ffmpeg parameter "-c:v libaom-av1".

I would suggest you to remove it.

[karaggeorge]

Hey @marlukcz

What format did you have selected when you did the export? From the options you've provided it looks like you had AV1 selected, which is a newer format (the newest we support) and is known to have long conversion times. Removing the -c:v libaom-a1 would mean we were converting to h264 instead of av1, which would be much faster, but would defeat the purpose by not resulting in a AV1 file. If you just want a h264 mp4 file as the result, you can select that option in the editor dropdown, which will indeed run only with the options you mentioned in your first conversion and will be much much faster.

We try to use the best options for each format we support, but some are inherently slower than others but provide different benefits. For AV1 specifically, the main benefit is the following:

Besides being royalty-free and open-source friendly, AV1 needs to actually offer advantages over already established technologies. Aomedia (the guardians of AV1 codec) claim it offers 30% better compression than H.265. That means it uses less data while offering the same quality for 4K UHD video.

So you sacrifice the conversion speed up front, in order to produce a smaller size result if file size is super important to you.

[karaggeorge]

Maybe we can do something to note the differences between h264 and av1 for users that don't necessarily know the difference, since both result in a .mp4 file. Not sure a good way to do that in the editor.

cc @skllcrn @sindresorhus

[marlukcz]

@karaggeorge true, I was converting to av1 ... I didn't notice it at first.
I am not aware to change it ever ... but maybe I did. What is default ?

Maybe you should make the title "AV1 - better but slower compression"

Conversion to h264 is much much faster. Like 100 times faster :-D

[sindresorhus]

I think we should show a Dialog the first time the user chooses AV1 that warns them how much slower AV1 is to encode.

[karaggeorge]

@marlukcz I feel like if it's your first time exporting AV1 would be on top alphabetically, but in general we sort formats by last used.

[apkoponen]

I just installed Kap and converting a 0:40 screen recording to MP4 (AV1 or H264) Takes more than 30 mins.

[weisjohn]

confirming the av1 issue speed. h264 is fine.

this article seems to indicate you may be able to shave down that compression time by bumping up the # of CPUs used https://www.streamingmedia.com/Articles/ReadArticle.aspx?ArticleID=130284