Kwave 24.12.1 slow performance

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1

Hello,
I’m using Kwave 24.12.1 installed as Snap package on Kubuntu 24.10.

I tried to open the following .mp3 file (an episode of a podcast) in Kwave

I can’t even start the playback because it’s soooo slow. It seems to play at 0.25x speed.
Can anyone try to open it and start the playback?

I tried to:

  • open another mp3 song on 24.12.1 and it works fine.
  • open the mp3 file above in kwave 23.08.5 (using APT) an it works fine

So I can’t understand if it’s a snap-package issue or what.

2

I thought that Kubuntu used apt for package management:

apt install kwave

Try it :wink:

3

Hello, I tried the apt package but it’s really old (23.08.5).
This old version works fine, but I can’t install the 24.12.1 version via apt.

4

What playback method are you using? Settings → Playback. Try Pulse Audio or ALSA if you’re not already. For me it plays with either of them. The Qt Multimedia backend is not very high performance, but it can work with smaller files and larger buffer sizes.

If you want to try the current development version, there is a nightly flatpak available now:
https://markpenner.space/blog/2025-01-06-kwave-flatpak/

5

Hello, thanks for the tip. ALSA and OSS (Open Sound System) return an error and they can’t be used, but I can use Pulse Audio which is much better.

Using Pulse Audio the playback is smooth, but the UI is very slow… it takes 2-3 seconds to open the menus (File, Edit, View, …). It’s a good performance improvement, but the software is still not usable.
It has a huge memory usage

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I’ve also tried to install flatpak but the nightly returns an error. FYI:

kf.dbusaddons: Failed to register name 'org.kde.kwave' with DBUS - does this process have permission to use the name, and do no other processes own it already?

please consider that I didn’t have flatpak installed so I may have some package missing

6

I wouldn’t expect OSS to work unless you intentionally set up your system to use it. OSS has been deprecated on Linux for many years, replaced by ALSA. I’m curious what was the error with ALSA?

Someday™ I want to look into the UI performance while playing. I’m guessing it’s probably redrawing or recalculating more than it would have to each screen update. The waveform display and playback position line are jumpy also. I just do my work while it’s not playing.

Kwave loads the whole (uncompressed) file into memory. It would be good if it could stream the file, but I think that would involve rewriting large parts of the codebase.

Interesting, I haven’t seen that error. Did you have another instance of Kwave already open?

7

In the terminal I see this:

--- SIGHUP ---

PlayBackPulseAudio: PA_CONTEXT_TERMINATED
PlayBackPulseAudio: mainloop freed
SAVE:    'pulseaudio' (3) -> '(Usa le impostazioni predefinite del server)'
PlayBackPlugin::createDevice('alsa' [4])
RESTORE: 'alsa' (4) -> ''
no soundcards found...
PlayBackDialog::setDevice(): '' -> ''
no soundcards found...
no soundcards found...
PlayBackALSA::alsaDeviceName('') - NOT FOUND
PlayBackDialog::setBitsPerSample(): 32 -> 32
no soundcards found...
PlayBackALSA::alsaDeviceName('') - NOT FOUND
PlayBackDialog::setChannels(): 2 -> 2
new playback params: '4','','2','32','10'

When I click “play” it says the device <> can’t be opened, no such file or directory

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ALSA in the flatpak works fine:

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immagine420×297 18.8 KB

While in the snap package I can’t see the devices:

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immagine507×256 7.85 KB

I tried to connect the alsa snap interface to Kwave but it fails

sudo snap connect kwave:alsa
error: snap "kwave" has no plug named "alsa"

Anyway, it’s not a big issue because I tested both systems (pulseaudio and alsa) in the flatpak and I can’t notice any difference on performance. They are similar so I can use pulse audio in the snap package, ignoring Alsa.

Thanks. I’ve only 8GB of RAM so it may not help, but System Monitor says that I’m only using 5GB out of 8GB (including 1.2GB used by Kwave).

When the playback is stopped, the menus are much more responsive and they open quickly, but moving in the timeline is still slow. If I click on any point of the sound track, I need to wait ~1 second to see the cursor moving to the new point. Not a big issue, I’m just curious if this is related to the uncompressed file or to the low RAM available.

Yes, you are right.

  • If I try to start Kwave while the Snap is opened, the flatpak doesn’t start and I get the error above.
  • If I try to start Kwave while the Apt version is openened, the flatpak doesn’t start and I don’t get any message in the terminal. It just closes.

Thanks for your replies

8

That all sounds like a snap packaging issue. I didn’t do the snap packaging and am not familiar with it, so not sure I can help there.

Actually I think that’s the same issue as the poor UI performance while playing, it’s just taking too much time to redraw the waveform.

Ok, I haven’t used the snap, so that would explain why I haven’t seen that error. Kwave does make sure there is only one instance running. I’m not sure if that’s necessary or not, it could be another instance would overwrite some settings the first instance was using or something.

You’re welcome, and thank you for following up with more details!

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