Tracker Cutting Howto

When we talk about “cutting a video”, we mean a highly automated process how the intro and outro get added to a recorded lecture using the CRS Ticket Tracker. Cutting in our case bascially only consists of setting the actual start and end of the lecture. Everything else is an automated process.

This page is meant to describe the steps involved when everything else is already prepared. See Intro-Outro-Generator for a way to generate intros based on a talk schedule and Project setup for the steps to set up a new tracker project (which is usually done by the “VOC event lead/ resposible person”).

There are two main ways of cutting a video: Using the KDEnlive or Shotcut open source video editors or by manually writing frame numbers to obtained from a video player like mpv the in- and outframe files.

General preconditions:

• Access to VOC VLAN or ethernet network
  • via DHCP or
  • fixed IP configured as secondary ethernet interface
• Account on https://tracker.c3voc.de
• Have VLC installed
• On Linux: Install cifs-utils (or similar) to mount the SMB share
• On Linux: Install KDEnlive (versino 17.x or 18.x) or Shotcut (version 22.12.21 is known to work)
• On Windows/ macOS: Install Shotcut as described at their website (Version 22.12.21 is known to work)

First of all, you need to mount the storage device's SMB file share to access the files:

• Linux:

  mkdir -p /video
  mount -t cifs -o uid=$USER,password=,ro "//storage.lan.c3voc.de/video" /video
  mount -t cifs -o uid=$USER,password=,rw "//storage.lan.c3voc.de/tmp" /video/tmp
  mount -t cifs -o uid=$USER,password=,rw "//storage.lan.c3voc.de/fuse" /video/fuse

• macOS: Open Finder, click “Connect to Server” (cmd+K) in the “Go To” menu and connect to smb://voc@storage.lan.c3voc.de/fuse
• Windows: Connect to the \\storage.lan.c3voc.de/video/ network drive

If you can see files in fuse/<EVENT>/<ROOM>/<Talk-ID>, you're ready to go.

To cut a lecture:

• Open https://tracker.c3voc.de and open an event/ project
• Click “recording task to cut” on the right to get a list of open cutting tickets
• Press the “cut” button and remember the talk ID
• Open /video/fuse/<EVENT>/<ROOM>/<Talk-ID>/ in some file explorer
• Open the uncut.ts with VLC:
  • Check if the start and end are present in the file. If not, go back to the tracker and click “extend timeline”
  • If translations are provided at the event: Check which tracks contain audio and which languages are spoken
• Start cutting with KDEnlive, Shotcut or mpv (see below)
• Check if audio and video are in sync
• Go back to the tracker to finish cutting:
  • Select language(s) from the drop-down using the right order (audio track 1, 2, 3)
  • If there was A/V-delay, enable the corresponding checkbox and set the number (VLC and mpv values need to be inverted)
  • click “finish”

Open the project.kdenlive project file to start cutting:

• Find start and end of the lecture and resize the bar by dragging the start and end with your mouse
  • When hovering over the ends, a green arrow should appear. Use this to change the length. It may snap at your current playback position.
  • Be careful to not move the video in the timeline
• Save the project file

If you have a poor connection to the storage, deactivate the video and audio thumbnails using the buttons on the right side of the lower window border.

Open the project_shotcut.mlt project file to start cutting:

• Skim through the recording (use <space> for play/pause)
  • Set start (in-point) with shortcut i
  • Set end (out-point) with shortcut o
• Save the project file

More shortcuts:

• i: Set start/ in-point
• o: Set end/ out-point
• <space>: play/ pause
• <page-up> <page-down>: Jump +/- 1 second (combine <Ctrl> or <ALT> to jump 2 or 5 seconds)
• <ALT>+<arrow-left>: Jump to start
• <ALT>+<arrow-right>: Jump to end
• <arrow-left> <arrow-right>: Jump 1 frame back/ forwards
• j / l: Fast back/ forwards (gets faster, if pressed multiple times)

Possible issues at installation:

• Error “This application failed to start because it could not find or load the Qt platform plugin “xcb” in […]”:

  • apt-get install libQt5Gui

    (see http://stackoverflow.com/questions/17106315/failed-to-load-platform-plugin-xcb-while-launching-qt5-app-on-linux-without)

If you like the command line, you can also configure mpv to show frame numbers by adding these settings in ~/.config/mpv/mpv.conf:

osd-level=3
osd-status-msg=${playback-time/full} / ${duration} (${percent-pos}%)\nframe: ${estimated-frame-number} / ${estimated-frame-count}

Open the uncut.ts in mpv to start cutting:

• Skim through the video to find the start
  • Write the frame number to the inframe file using echo <FRAME> > /video/fuse/<EVENT>/<ROOM>/<Talk-ID>/inframe
• Do the same for the end using the outframe file

Using “echo” works best since some text editors like to create temporary lock files which isn't allowed on the FUSE file system.

Additional keyboard shortcuts: See https://mpv.io/manual/master/#keyboard-control

• Shotcut or VLC don't show a time during playback:

  • The uncut.ts has broken timestamps because the recording was stopped to early or started to late. See defekte_timestamps.
  • Skimming though the video leads to jumps or some parts of the video can't be jumped to:
  • The uncut.ts has broken timestamps because the recording was stopped to early or started to late. See defekte_timestamps.
  • SMB connect fails on OS X 10.11 El Capitan: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=821730
  • Add an SMB password to the voc user with smbpasswd -a voc to that one can be used instead of the guest user

The uncut.ts can get quite large as we're still recording using the MPEG2 codec. If you need to cut via the VPN, it may be useful to generate smaller low-resolution “proxy” files and cut based on that:

• press “cut” in the tracker to assign the ticket to yourself
• create a proxy file from /video/fuse/…/uncut.ts: webcut_lores_mp4
• copy the KDEnlive or Shotcut project file to your local file system and replace the video URL
• open the project and cut
• upload the project file to the FUSE file system, e.g. by:
  • loading the file to your home directory on the storage server/ encoder
  • cat meinfile.mlt > /video/fuse/…/project_shotcut.mlt (or similar for KDEnlive)
• click “finish” in the tracker