Ubuntu – All video thumbnails fail to be generated

First, make sure all the ffmpeg (the back of vlc) components you need are installed:

sudo apt-get install ffmpeg ffmpegthumbnailer gstreamer0.10-ffmpeg

Clear the thumbnail cache, with bleachbit, ubuntu tweak, or this command:

rm ~/.thumbnails/fail/gnome-thumbnail-factory/*
rm ~/.thumbnails/normal/*

Now we need to tell Ubuntu not to use totem, but to use ffmpeg instead.
sudo nano /usr/share/thumbnailers/totem.thumbnailer and replace all the ext in totem.thumbnailer with the following:

[Thumbnailer Entry]
TryExec=ffmpegthumbnailer
Exec=ffmpegthumbnailer -s %s -i %i -o %o -c png -f -t 10
MimeType=application/mxf;application/ogg;application/ram;application/sdp;application/vnd.ms-wpl;application/vnd.rn-realmedia;application/x-extension-m4a;application/x-extension-mp4;application/x-flash-video;application/x-matroska;application/x-netshow-channel;application/x-ogg;application/x-quicktimeplayer;application/x-shorten;image/vnd.rn-realpix;image/x-pict;misc/ultravox;text/x-google-video-pointer;video/3gpp;video/dv;video/fli;video/flv;video/mp2t;video/mp4;video/mp4v-es;video/mpeg;video/msvideo;video/ogg;video/quicktime;video/vivo;video/vnd.divx;video/vnd.rn-realvideo;video/vnd.vivo;video/webm;video/x-anim;video/x-avi;video/x-flc;video/x-fli;video/x-flic;video/x-flv;video/x-m4v;video/x-matroska;video/x-mpeg;video/x-ms-asf;video/x-ms-asx;video/x-msvideo;video/x-ms-wm;video/x-ms-wmv;video/x-ms-wmx;video/x-ms-wvx;video/x-nsv;video/x-ogm+ogg;video/x-theora+ogg;video/x-totem-stream;audio/x-pn-realaudio;audio/3gpp;audio/ac3;audio/AMR;audio/AMR-WB;audio/basic;audio/midi;audio/mp2;audio/mp4;audio/mpeg;audio/ogg;audio/prs.sid;audio/vnd.rn-realaudio;audio/x-aiff;audio/x-ape;audio/x-flac;audio/x-gsm;audio/x-it;audio/x-m4a;audio/x-matroska;audio/x-mod;audio/x-mp3;audio/x-mpeg;audio/x-ms-asf;audio/x-ms-asx;audio/x-ms-wax;audio/x-ms-wma;audio/x-musepack;audio/x-pn-aiff;audio/x-pn-au;audio/x-pn-wav;audio/x-pn-windows-acm;audio/x-realaudio;audio/x-real-audio;audio/x-sbc;audio/x-speex;audio/x-tta;audio/x-wav;audio/x-wavpack;audio/x-vorbis;audio/x-vorbis+ogg;audio/x-xm;application/x-flac;

And exit nautilus:

nautilus -q

Go to you video and see the thumbnail preview appear for all videos.

Thumbnails of specific file types can be disabled using dconf editor.

Install dconf editor:

Hit Alt+Ctrl+T and run the following command:

sudo apt-get install dconf-tools

Or search for "dconf-tools" in Software Center and install it from there.

How to disable thumbnails of specific file type?

Once installed, Hit super key (windows key) to open Unity dash and search for "dconf editor" and open it.

Navigate to org > gnome > desktop > thumbnailer

Paste the MIME type of PDF 'application/pdf' in the value field of disable key.

This will prevent Nautilus from generating thumbnails of PDF's in the future but old thumbnails will be there. To solve this you'll have to clear Nautilus thumbnail cache.

Open your home directory and Hit Ctrl+H to show the hidden files and folders. Open .thumbnails and delete all the files in it.

Restart your system or kill Nautilus for change to take effect.

To disable thumbnails for other file types, Add there MIME type in disable list as described above. Seprate multiple types with comma. like this:

['application/pdf','image/jpeg','video/mp4']

For complete list of MIME types visit iana.org.