MKV and AVI thumbnails not working on macOS 26.0.1 (MP4 works fine)

[MichaelForestjump]

Hi, I'm using QLVideo 2.21 on macOS 26.0.1 (build 25A362) and MKV and AVI file thumbnails are not
appearing in Finder.

What works:
✅ QuickLook preview (spacebar) works perfectly for MKV and AVI files
✅ MP4 files show thumbnails correctly (using native macOS generator)
✅ All QLVideo extensions are enabled in System Settings
✅ Full Disk Access granted to QuickLook Video app

What doesn't work:
❌ MKV file thumbnails don't appear in Finder (showing generic MKV icon instead of video preview)
❌ AVI file thumbnails don't appear in Finder (showing generic AVI icon instead of video preview)
❌ Same issue on both APFS and ExFAT volumes
❌ Tried "Refresh" button - no effect
❌ Cleared QuickLook cache multiple times

System info:

• macOS: 26.0.1 (build 25A362)
• QLVideo: 2.21 (installed via Homebrew)
• Extensions visible in pluginkit -m:
  • com.apple.uk.org.marginal.qlvideo.thumbnailer
  • com.apple.uk.org.marginal.qlvideo.previewer

Note: Since MP4 thumbnails work but MKV and AVI thumbnails don't, this suggests the issue is
specifically with QLVideo's thumbnail extension on macOS 26. I suspect this might be related to
macOS 26 introducing new changes to the QuickLook system, similar to what happened with Sequoia
(15.x).

Is macOS 26 support planned? Any workarounds available?

[eirnym]

I have Sequoia and had to enable both QLVideo extensions in System Settings to work properly.

[Marginal]

@MichaelForestjump What media playing app are you using?

From the QuickLook Video app's Help menu, please choose Report an Issue.
Drop any problematic file and press Send.
Copy and paste the output below.

[metrodorian]

Same problem.
THX so much for making my life more beautiful. I am not sure, if you'll continue development as some features did now find their way into the OS.
Here is my output (MacOS 26.1):

---

QLVideo: 2.21
macOS: Version 26.1 (Build 25B78)
Hardware: Mac16,1 arm64 neon=yes
mdimport: Imported 'file.mkv' of type 'org.matroska.mkv' with plugIn /Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter. 43 attributes returned .

{
  "programs": [
  ],
  "stream_groups": [
  ],
  "streams": [
    {
      "codec_name": "h264",
      "profile": "Main",
      "codec_type": "video",
      "codec_tag_string": "[0][0][0][0]",
      "width": 1920,
      "height": 1080,
      "display_aspect_ratio": "16:9",
      "pix_fmt": "yuv420p",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "profile": "Dolby Digital Plus   Dolby Atmos",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "png",
      "codec_type": "video",
      "codec_tag_string": "[0][0][0][0]",
      "width": 350,
      "height": 197,
      "display_aspect_ratio": "350:197",
      "pix_fmt": "rgb24",
      "disposition": {
        "default": 0,
        "attached_pic": 1,
        "timed_thumbnails": 0
      }
    }
  ],
  "format": {
    "format_name": "matroska,webm",
    "duration": "3355.712000",
    "size": "2813964773",
    "bit_rate": "6708477",
    "probe_score": 100
  }
}

[Marginal]

I upgraded to macOS Vista Tahoe and I can reproduce this issue.

[metrodorian]

It started working again but I don't know why. Pretty sure Quicklook and MacOS are the same version.
Here's my dump.

Your description of the problem here!

---

QLVideo: 2.21
macOS: Version 26.1 (Build 25B78)
Hardware: Mac16,1 arm64 neon=yes
mdimport: Imported 'file.mkv' of type 'org.matroska.mkv' with plugIn /Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter. 43 attributes returned .

{
  "programs": [
  ],
  "stream_groups": [
  ],
  "streams": [
    {
      "codec_name": "h264",
      "profile": "Main",
      "codec_type": "video",
      "codec_tag_string": "[0][0][0][0]",
      "width": 1920,
      "height": 1080,
      "display_aspect_ratio": "16:9",
      "pix_fmt": "yuv420p",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "eac3",
      "profile": "Dolby Digital Plus   Dolby Atmos",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "5.1(side)",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "subrip",
      "codec_type": "subtitle",
      "codec_tag_string": "[0][0][0][0]",
      "disposition": {
        "default": 0,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "png",
      "codec_type": "video",
      "codec_tag_string": "[0][0][0][0]",
      "width": 350,
      "height": 197,
      "display_aspect_ratio": "350:197",
      "pix_fmt": "rgb24",
      "disposition": {
        "default": 0,
        "attached_pic": 1,
        "timed_thumbnails": 0
      }
    }
  ],
  "format": {
    "format_name": "matroska,webm",
    "duration": "3355.712000",
    "size": "2813964773",
    "bit_rate": "6708477",
    "probe_score": 100
  }
}

[LooneyH]

I've had a similar problem, where the icon previews are working but the actual preview isn't playing. Here's the log of the file that failed (I wonder if it's the fact it's mkv and webm together?)

---

QLVideo: 2.21
macOS: Version 26.1 (Build 25B78)
Hardware: Mac15,6 arm64 neon=yes
mdimport: Imported 'file.mkv' of type 'org.matroska.mkv' with plugIn /Applications/QuickLook Video.app/Contents/Library/Spotlight/Video.mdimporter. 38 attributes returned .

{
  "programs": [
  ],
  "stream_groups": [
  ],
  "streams": [
    {
      "codec_name": "h264",
      "profile": "High",
      "codec_type": "video",
      "codec_tag_string": "[0][0][0][0]",
      "width": 1920,
      "height": 1080,
      "display_aspect_ratio": "16:9",
      "pix_fmt": "yuv420p",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    },
    {
      "codec_name": "vorbis",
      "codec_type": "audio",
      "codec_tag_string": "[0][0][0][0]",
      "sample_fmt": "fltp",
      "channel_layout": "stereo",
      "disposition": {
        "default": 1,
        "attached_pic": 0,
        "timed_thumbnails": 0
      }
    }
  ],
  "format": {
    "format_name": "matroska,webm",
    "duration": "70.003000",
    "size": "25780726",
    "bit_rate": "2946242",
    "probe_score": 100
  }
}

[JiDoan]

Not sure if it is related to this issue but I updated to macOS Tahoe 26.1 and my Spotlight began to crash with QLVideo's Spotlight extension enabled in System Preferences. Thumbnails still appear to work for me though. Crash logs suggest that some timestamp may be malformed? Running mdimporter seems to yield nothing suspicious.

Spotlight crash logs in Console:
Exception Reason: -[__NSCFString timeIntervalSinceDate:]: unrecognized selector sent to instance 0x9d9e624f0

mdimporter:

Imported '/private/tmp/MVI_1117.AVI' of type 'public.avi' with no plugIn.
28 attributes returned
{
    ":MD:DeviceId" = 16777230;
    ":MD:kMDItemPath" = "/private/tmp/MVI_1117.AVI";
    "_kMDItemContentChangeDate" = "2009-11-21 02:39:00 +0000";
    "_kMDItemCreationDate" = "2009-11-21 02:39:00 +0000";
    "_kMDItemCreatorCode" = 0;
    "_kMDItemDisplayNameWithExtensions" =     {
        "" = "MVI_1117.AVI";
    };
    "_kMDItemFileName" = "MVI_1117.AVI";
    "_kMDItemFinderFlags" = 0;
    "_kMDItemFinderLabel" = 0;
    "_kMDItemFromImporter" = 1;
    "_kMDItemIsEvictedFile" = "<null>";
    "_kMDItemIsExtensionHidden" = 0;
    "_kMDItemIsFromImporter" = 1;
    "_kMDItemOwnerGroupID" = 0;
    "_kMDItemOwnerUserID" = 501;
    "_kMDItemPluginDisabledBTM" = 1;
    "_kMDItemTypeCode" = 0;
    "com_apple_metadata_modtime" = 280463940;
    kMDItemContentCreationDate = "2009-11-21 02:39:00 +0000";
    kMDItemContentModificationDate = "2009-11-21 02:39:00 +0000";
    kMDItemContentType = "public.avi";
    kMDItemContentTypeTree =     (
        "public.avi",
        "public.movie",
        "public.audiovisual-content",
        "public.data",
        "public.item",
        "public.content"
    );
    kMDItemDateAdded = "2025-11-25 06:17:01 +0000";
    kMDItemDisplayName =     {
        "" = "MVI_1117.AVI";
    };
    kMDItemDocumentIdentifier = 0;
    kMDItemKind =     {
        "" = "AVI movie";
        ar = "\U0641\U064a\U0644\U0645 AVI";
        ca = "V\U00eddeo AVI";
        cs = "Film AVI";
        da = "AVI-film";
        de = "AVI-Film";
        el = "\U03a4\U03b1\U03b9\U03bd\U03af\U03b1 AVI";
        en = "AVI movie";
        "en_AU" = "AVI movie";
        "en_GB" = "AVI movie";
        es = "V\U00eddeo AVI";
        "es_419" = "Video AVI";
        "es_US" = "Video AVI";
        fi = "AVI-elokuva";
        fr = "Vid\U00e9o AVI";
        "fr_CA" = "Vid\U00e9o AVI";
        he = "\U05e1\U05e8\U05d8 AVI";
        hi = "AVI \U092b\U093c\U093f\U0932\U094d\U092e";
        hr = "AVI film";
        hu = "AVI film";
        id = "Film AVI";
        it = "Filmato AVI";
        ja = "AVI\U30e0\U30fc\U30d3\U30fc";
        ko = "AVI \Ub3d9\Uc601\Uc0c1";
        ms = "Filem AVI";
        nl = "AVI-film";
        no = "AVI-film";
        pl = "film AVI";
        "pt_BR" = "Filme AVI";
        "pt_PT" = "Filme AVI";
        ro = "film AVI";
        ru = "\U0412\U0438\U0434\U0435\U043e AVI";
        sk = "AVI film";
        sl = "Film AVI";
        sv = "AVI-film";
        th = "\U0e20\U0e32\U0e1e\U0e22\U0e19\U0e15\U0e23\U0e4c\U0e41\U0e1a\U0e1a AVI";
        tr = "AVI filmi";
        uk = "\U0424\U0456\U043b\U044c\U043c AVI";
        vi = "Phim AVI";
        "zh_CN" = "AVI\U5f71\U7247";
        "zh_HK" = "AVI\U96fb\U5f71";
        "zh_TW" = "AVI\U5f71\U7247";
    };
    kMDItemLogicalSize = 20208542;
    kMDItemPhysicalSize = 20201472;
}