Cover art cause exporting endless for webm

Bug
1

  • What is your operating system?

Ubuntu 26.04

  • What is your Shotcut version (see Help > About Shotcut)?

$ snap list  shotcutName     Version  Rev   Tracking       Publisher   
Notesshotcut  26.5.1   2205  latest/stable  meltytech✓  classic

  • Can you repeat the problem? If so, what are the steps?

  1. Generate reference input video and reference cover-art
ffmpeg -f lavfi -i testsrc=size=406x720:rate=1:duration=10 -c:v libvpx-vp9 -pix_fmt yuv420p output406.webm
magick -size 406x720 xc:gray +noise gaussian cover.jpg
  1. Make project, put reference video on the timeline and make job using my “webm_cover” preset. It will works like a charm
  2. Go to Metadata tab and in “Cover art“ filed add path to cover.jpg
  3. make job, exports will never end with log
[webm @ 0x77c520200980] Only VP8 or VP9 or AV1 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM.
[consumer avformat] Could not write header '/home/a/mystorage/FireFox_Downloads/shotcut_bug/shotcut_bug.webm'
[AVIOContext @ 0x77c5203eca40] Statistics: 275 bytes written, 0 seeks, 1 writeouts

The bug1 is that export will never end. Bug2 - it should be possible to add cover art to webm. I also have feature request, is it possible to disable message “Only VP8 or VP9 or AV1 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM” when user doesn’t use audio and subtitles?

Cover art cause exporting endless for webm.zip (157.1 KB)

2

The latest daily build does not reproduce this. Instead, I get in the export job log with the cover.jpg you provided:

[consumer avformat] attached_pic: output format ‘webm’ does not support codec ‘mjpeg’; ignoring cover art

Same goes for PNG. WebM might only support WebP, but the MLT layer (“[consumer avformat]”) does not support WebP at this time. According to the answer at https://stackoverflow.com/a/65713819 WebM does not support cover art at all. Switching Format to ma\troska works:

[consumer avformat] attached_pic: detected dimensions 406x720 for ‘/home/ddennedy/Downloads/cover.jpg’
[consumer avformat] attached_pic: added cover art from ‘/home/ddennedy/Downloads/cover.jpg’

is it possible to disable message “Only VP8 or VP9 or AV1 video and Vorbis or Opus audio and WebVTT subtitles are supported for WebM”

No. That message comes from a FFmpeg library, and it provides a strong hint about a problem. I do not reproduce it from your preset, but I do see that Export > Audio is disabled. If I enable it, the codec in your preset is AAC, and I get this message. AAC is not supposed to be used in WebM.