With both a 15.12.3 under Ubuntu 16.04 and a 17.08.2 under Ubuntu 17.10 I run into the same problem: I'd like to record audio tracks (voice comment) to be added on videos, and I have configured kdenlive in the configuration settings to just record audio, no video, and appropriate audio devices (pavucontrol shows kdenlive is properly connected), but as soon as I press the record button I get an error message Capture crashed, please check your parameters without further hints. A problem might be that kdenlive leaves the choice between Webcam and Screen Grab only in the input selector.
Just for testing I've added a real videocam to make /dev/video0 appear. Again, kdenlive issues that error message, but once I check the video button, it starts to records (with video), and then crashes with a segfault.
The problem persists with a kdenlive built from git Applications/18.08 with (largely) Debian stretch plus MLT backported from Debian sid just about now. And it's fairly annoying as it kills the old "let your father edit his videos" use case. Again, to reproduce: go to clip monitor, click the cross button, uncheck video, check audio, hit record. I'm seeing "Capture crashed, please check your parameters" (and I'd be very interested in circumstances if you don't). The only perhaps unusual aspect of the box is that there's no pulseaudio running (but I *think* I've seen it on a pa-running box, too); the message is invariant to any profile changes (channels, source, encoding profile). I've tried overriding the profiles under the assumption that they may somehow become ffmpeg command lines (which, judging from recipes floating around on the net, they've probably been at some point, right?). To no avail. So, it'd be great if someone in the know could comment if this is even supposed to work at this point and if so, what one could try to make it work or at least figure out what "crashes" and why. Wishlist item: Generate less mystifying diagnostics on this, at least on stderr...
Looking a bit more closely, I see that in recmanager.cpp, createV4LProducer, there's code like this: Mlt::Producer *prod = nullptr; if (m_recVideo->isChecked()) { (...) } if (m_recAudio->isChecked() && prod && prod->is_valid()) { (...) } return prod; Since prod can only be non-null in the second check when m_recVideo->isChecked(), there's no way to have audio-only recording with 18.08, is there? Does anyone understand why things were written like this?
It seems that this report is related to very old unmaintained version. A lot changed since then, especially the timeline got a complete rewrite and it is likely that this has been fixed. Feel free to reopen this bug or create a new report if this is still happening with the latest version (https://kdenlive.org/en/download/)