Bug 430093 - Webm high quality worse with Quality at highest setting (recent regression)
Summary: Webm high quality worse with Quality at highest setting (recent regression)
Alias: None
Product: kdenlive
Classification: Applications
Component: Video Display & Export (show other bugs)
Version: 20.08.3
Platform: Flatpak Linux
: NOR critical
Target Milestone: ---
Assignee: Jean-Baptiste Mardelle
Depends on:
Reported: 2020-12-06 21:13 UTC by Eric Mesa
Modified: 2022-05-22 11:37 UTC (History)
3 users (show)

See Also:
Latest Commit:
Version Fixed In: 22.04.0


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Description Eric Mesa 2020-12-06 21:13:22 UTC
Created a Webm with quality slider all the way to the right and the quality looks horrendous. Very pixelated. This wasn't happened a few days ago before I updated to the latest. This is on flatpak so I don't know if the change is from kdenlive or the ffmpeg in flatpak, but the issue kind of seems similar to what was mentioned https://bugs.kde.org/show_bug.cgi?id=357153, but that's a super old bug. So I think this is a regression or a change in hw ffmpeg is interpreting the slider.

I put critical because no one wants to wait 2 hour for a render to end up with a shit quality video.

1. Setup kdenlive with your video
2. Tell it to render webm
3. Set quality slider to the highest setting
4. render

Very, very splotchy video with bad quality 

Really awesome video with great quality

Linux/KDE Plasma: Fedora 32
(available in About System)
KDE Plasma Version: 5?
KDE Frameworks Version: 5.76
Qt Version: 5.15.2

using flatpak
Comment 1 Eric Mesa 2020-12-07 00:13:52 UTC
I did a few more tests and I would like to modify the issue slightly. A lower quality bar does not improve the quality. However, switching from webm to mp4 produces the quality I'd expect. These are all under the "Generic" set of output. That is to say, WebM (VP8/Vorbis) and Mp4 (H264/AAC). 

For more concrete example of how wrong thigns are with Webm:

Before I had this issue, I created a 34 minute video with WebM slider at highest quality. The file size was 2.0GB. After having this issue, I created a 40 minute video with WebM at the highest quality. It was 303 MB.
Comment 2 contact 2021-06-18 23:26:00 UTC
I really want to bump this- this is still a problem, even in the latest Kdenlive. I'm running Kdenlive 21.04.2 on Arch Linux with MLT 6.26.1. This happens with the daily AppImage kdenlive-21.07.70-ee7a141-x86_64.appimage too.

I can confirm kdenlive-19.12.0a-x86_64.appimage works.
Comment 3 contact 2021-06-19 00:01:44 UTC
Exporting the project then running using melt gives this error:

[libvpx @ 0x7f7ef0001d00] Bitrate not specified for constrained quality mode, using default of 256kbit/sec

Changing vb="0" to vb="10M" helps.

Exporting the project from a working Kdenlive also gives the same issue and poor output.

It looks like this may be a behaviour change in ffmpeg:


Setting 'vb=1M' in the export helps, but it still doesn't look proper.
Comment 4 Jens Reimann 2021-09-22 08:26:12 UTC
I just ran into the same problem. Taking a look at the logs I see:

Started render process: /app/bin/melt -progress /var/tmp/kdenlive-TZQHdn.mlt out=20326
[libvpx @ 0x7fa03c003940] Application has requested 24 threads. Using a thread count greater than 16 is not recommended.
[libvpx @ 0x7fa03c003940] Bitrate not specified for constrained quality mode, using default of 256kbit/secJob aborted by user

So it looks like some argument is missing and it defaults to some bad quality defaults.
Comment 5 Bug Janitor Service 2022-01-22 19:11:07 UTC
A possibly relevant merge request was started @ https://invent.kde.org/multimedia/kdenlive/-/merge_requests/271
Comment 6 Julius Künzel 2022-01-23 00:36:25 UTC
Git commit d6910eacb8cda27adaf63afcec76e3391da4b2b7 by Julius Künzel, on behalf of Farid Abdelnour.
Committed on 23/01/2022 at 00:35.
Pushed by jlskuz into branch 'master'.

Try to improve alpha render quality

Should fix bad quality renders in videos with alpha profile.

Fixes #1075 
Related: bug 436879, bug 357153

M  +4    -6    data/profiles.xml

Comment 7 contact 2022-01-23 06:44:47 UTC
Still broken as of git.
Comment 8 Eric Mesa 2022-05-14 19:35:23 UTC
I believe this is now fixed in 22.04 Flatpak.