Dolphin – How to Fix Thumbnails Not Showing in Dolphin

dolphinkdekubuntuthumbnailsunity

I have changed my Unity default file manager to Dolphin.

Problem: video thumbnails don't show up anymore.
In Nautilus the thumbnails are shown correctly.

How to make Dolphin show thumbnails?

Best Answer

Thumbnailer

To show thumbnails the Dolphin will need the thumbnail plug in.

enter image description here

Video thumbnailers for the Dolphin:

:~$ apt-cache show ffmpegthumbs
Package: ffmpegthumbs
Priority: optional
Section: universe/kde
...
Description: video thumbnail generator using ffmpeg
 FFMpegThumbs is a video thumbnail generator for KDE file managers
 like Dolphin and Konqueror.  It enables them to show preview images
 of video files using FFMpeg.
 .
 This package is part of the KDE multimedia module.

Homepage: http://www.kde.org/

:~$ apt-cache show mplayerthumbs
Package: mplayerthumbs
Priority: optional
Section: universe/kde
...
Description: video thumbnail generator using mplayer
 MPlayerThumbs is a video thumbnail generator for KDE file managers
 like Dolphin and Konqueror.  It enables them to show preview images
 of video files using MPlayer.
 .
 This package is part of the KDE multimedia module.

Homepage: http://www.kde.org/

:~$ apt-cache show kffmpegthumbnailer
Package: kffmpegthumbnailer
Priority: extra
Section: universe/kde
...
Description: video thumbnailer for KDE
 kffmpegthumbnailer is a video thumbnailer based on ffmpegthumbnailer.
 The thumbnailer uses ffmpeg to decode frames from the video files.

Homepage: http://www.kde-apps.org/content/show.php/kffmpegthumbnailer?content=117562

Settings

To use the thumbnail you need to enable the thumbnailer from the Dolphin settings.

enter image description here

Introduction

So it turns out that KDE and GNOME now follow slightly different thumbnail naming and metadata conventions. This is quite unfortunate since issues like these were supposed to be eliminated with the work of the Free Standards Group.

I've filed a bug report with KDE that will hopefully get this addressed eventually, but for now thumbnails generated by KDE and GNOME are sadly incompatible with each other.

Thumbnailer script to bridge the KDE/GNOME gap

In order to work around this incompatibility, I ended up modifying the Python script that James Henstridge posted in the Q&A linked to above. The main change I implemented is a function that updates the generated thumbnails to be recognized by KDE (by renaming them and updating the PNG metadata chunk).

Here is the aforementioned script in its current revision:

#!/usr/bin/python3

"""
Thumbnail generator for KDE/GNOME

Largely based on a script by James Henstridge
(https://askubuntu.com/a/201997)

Unfortunately there seems to be some disagreement between GNOME and KDE
towards how to follow the XDG specs for saving thumbnails. This script
is meant as a workaround to that issue, generating thumbnails that follow
both specifications.

Dependencies: python3 gir1.2-gnomedesktop-3.0 python-pillow

pillow can be installed with `pip install pillow`

You will also need to have the corresponding thumbnailers installed (e.g.
evince-thumbnailer). KDE thumbnailers are not supported. All previews are
generated through GNOME's thumbnail factory and then made compatible with KDE.

Further references:

Thumbnail specifications in KDE/GNOME:

- https://bugs.kde.org/show_bug.cgi?id=393015
- https://api.kde.org/frameworks/kio/html/previewjob_8cpp_source.html
- https://lazka.github.io/pgi-docs/GnomeDesktop-3.0/classes/DesktopThumbnailFactory.html

Setting PNG metadata:

- http://pillow.readthedocs.io/en/5.1.x/PIL.html#PIL.PngImagePlugin.PngInfo
- https://stackoverflow.com/a/10552742/1708932

Copyright: (c) 2012 James Henstridge <https://launchpad.net/~jamesh>
           (c) 2018 Glutanimate <https://glutanimate.com/>
License: MIT license
"""

import os
import sys
from hashlib import md5

from PIL import Image
from PIL import PngImagePlugin

import gi
gi.require_version('GnomeDesktop', '3.0')
from gi.repository import Gio, GnomeDesktop

# FIXME: Hardcoding the Thumbnailer to a generic name
#        regardless of MIME type might not always work
KDE_THUMBNAILER = "KDE Thumbnail Generator"


def update_name_and_meta(thumb_path, filename, mtime, mime_type, size):
    print("Making thumb compatible with KDE...")
    abs_path = os.path.abspath(filename)
    # The spaces in our URI are not escaped. This is not in accordance
    # with the URI RFC2396 which is listed in the freedesktop specs,
    # but it's what KDE currently uses 
    # (cf.: https://bugs.kde.org/show_bug.cgi?id=393015)
    kde_uri = "file://" + abs_path  
    kde_md5 = md5(kde_uri.encode("utf-8")).hexdigest()
    thumb_dir = os.path.dirname(thumb_path)
    kde_thumb_path = os.path.join(thumb_dir, kde_md5 + ".png")

    if os.path.exists(kde_thumb_path):
        print("KDE thumb already exists. Skipping")
        return

    im = Image.open(thumb_path)

    # Set PNG metadata chunk
    meta = PngImagePlugin.PngInfo()
    meta.add_itxt("Software", KDE_THUMBNAILER)
    meta.add_text("Thumb::MTime", str(int(mtime)))
    meta.add_text("Thumb::Mimetype", mime_type)
    meta.add_text("Thumb::Size", str(size))
    meta.add_itxt("Thumb::URI", kde_uri)

    im.save(kde_thumb_path, "png", pnginfo=meta)

    # uncomment this to remove GNOME thumbnails:
    # os.remove(thumb_path)


def make_thumbnail(factory, filename):
    mtime = os.path.getmtime(filename)
    # Use Gio to determine the URI and mime type
    f = Gio.file_new_for_path(filename)
    uri = f.get_uri()
    info = f.query_info(
        'standard::content-type', Gio.FileQueryInfoFlags.NONE, None)
    mime_type = info.get_content_type()
    size = info.get_size()

    if factory.lookup(uri, mtime) is not None:
        print("FRESH       %s" % uri)
        return False

    if not factory.can_thumbnail(uri, mime_type, mtime):
        print("UNSUPPORTED %s" % uri)
        return False

    thumbnail = factory.generate_thumbnail(uri, mime_type)
    if thumbnail is None:
        print("ERROR       %s" % uri)
        return False

    factory.save_thumbnail(thumbnail, uri, mtime)

    thumb_path = factory.lookup(uri, mtime)
    update_name_and_meta(thumb_path, filename, mtime, mime_type, size)

    print("OK          %s" % uri)

    return True


def thumbnail_folder(factory, folder):
    for dirpath, dirnames, filenames in os.walk(folder):
        for filename in filenames:
            make_thumbnail(factory, os.path.join(dirpath, filename))


def main(argv):
    factory = GnomeDesktop.DesktopThumbnailFactory()
    for filename in argv[1:]:
        if os.path.isdir(filename):
            thumbnail_folder(factory, filename)
        else:
            make_thumbnail(factory, filename)


if __name__ == '__main__':
    sys.exit(main(sys.argv))

Installation

Copy and paste the code section above into a new file, choose a fitting name for it (e.g. thumbnailer), and mark it executable.

Dependencies

For the script to work properly you will need to have the python bindings for GNOME installed. The script also depends on Python's pillow library which may be installed via pip.

The following commands should take care of all dependencies:

sudo apt install gir1.2-gnomedesktop-3.0 python3-pip
pip3 install pillow

Thumbnails are first generated through GNOME's thumbnail factory and then made compatible with KDE. So you will still need to have all the corresponding GNOME thumbnailer modules installed. KDE's own thumbnailers are not supported. E.g.: for the script to support generating PDF thumbnails you would have to install evince.

(I would have loved to use KDE's python bindings directly, but it looks like both pykde4 and pykde5 have been abandoned for years).

Usage

The general use is the same as with any other thumbnailing script. Just invoke it with the files or folders where you want to generate thumbnails as arguments, e.g.:

thumbnailer /home/Documents

References

Thumbnail specifications in KDE/GNOME:

Setting PNG metadata: