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Video files with AC3 audio open with ~ 20 s delay in vlc

  • Operating system: Fedora Linux 35 Beta
  • Wireplumber version: 0.4.2 (from official Fedora repositories)
  • Vlc version: 3.0.16 (from RPM Fusion repositories)

If Wireplumber is used, as Fedora Linux 35 Beta does by default, vlc has an about 20 second delay when opening video files that have an AC3 audio track. It is not clear how much this is a vlc issue and how much a Wireplumber issue, so I am reporting this to both. Vlc issue is 24993, (or rather, its coarse description seemed to fit the symptoms, so added my information there).

I have identified Wireplumber as having some role in this by switching back to pipewire-media-session as was used in Fedora 34. The issue disappears when I do that and reboot.

I have posted logs and such in the vlc issue. The difference between Wireplumber and pipewire-media-session seems to boil down to this: With Wireplumber, there is first a 20 second delay, then the following is printed and video starts to play (with working sound, despite sound related error messages):

[00005641f6aaf340] vlcpulse audio output error: digital pass-through stream connection failure: Timeout

With pipewire-media-session, there is no delay and that same line is printed earlier, with the difference that the error message is Input/Output error instead of Timeout.

Here are mkvinfo results from the problematic video, with some parts that seem unimportant and/or uniquely identifying removed:

$ mkvinfo video_bad.mkv
+ EBML head
|+ EBML version: 1
|+ EBML read version: 1
|+ Maximum EBML ID length: 4
|+ Maximum EBML size length: 8
|+ Document type: matroska
|+ Document type version: 2
|+ Document type read version: 2
|+ Seek head (subentries will be skipped)
|+ Segment information
| + Timestamp scale: 1000000
| + Multiplexing application: libebml v1.0.0 + libmatroska v1.0.0
| + Writing application: mkvmerge v4.0.0 ('The Stars were mine') built on Jun  6 2010 16:18:42
| + Track
|  + Track number: 2 (track ID for mkvmerge & mkvextract: 1)
|  + Track type: audio
|  + Codec ID: A_AC3
|  + Default duration: 00:00:00.032000000 (31.250 frames/fields per second for a video track)
|  + Audio track
|   + Sampling frequency: 48000
|   + Channels: 6

and for comparison, the same info from a Matroska file that plays without any delay:

$ mkvinfo video_good.mkv 
+ EBML head
|+ EBML version: 1
|+ EBML read version: 1
|+ Maximum EBML ID length: 4
|+ Maximum EBML size length: 8
|+ Document type: matroska
|+ Document type version: 4
|+ Document type read version: 2
|+ Seek head (subentries will be skipped)
|+ Segment information
| + Timestamp scale: 1000000
| + Multiplexing application: Lavf58.76.100
| + Writing application: Lavf58.76.100
|+ Tracks
| + Track
|  + Track number: 5 (track ID for mkvmerge & mkvextract: 4)
|  + "Lacing" flag: 0
|  + Language: und
|  + Codec ID: A_AAC
|  + Track type: audio
|  + Audio track
|   + Channels: 2
|   + Sampling frequency: 44100
|   + Output sampling frequency: 44100
|   + Bit depth: 32
|  + Codec's private data: size 2
Edited by Otto