Friday, 22 December 2017

Extract subtitles as SRT from mkv

mkvextract tracks source.mkv

You can obtain the track number using mkvtoolnix-gui or mkvinfo

Friday, 6 October 2017

Querying video file metadata with mediainfo

I am working on a script that will query media files (mp4/mkv videos) to obtain metadata that can be subsequently used to rename the file to enforce a naming convention. I use the excellent mediainfo tool (available in the standard repositories) to do this.

mediainfo has a metric tonne of options and functions that you can use for various purposes. In my case I want to know the aspect ratio, vertical height and video codec for the file. This can be done in a single command;

mediainfo --Inform="Video;%DisplayAspectRatio%,%Height%,%Format%"

This works fine and returns something like this;


When I say it works fine I mean it works fine in 99% of cases. The other 1% are made up of files that contain more than one video stream. Sometimes people package a JPEG image inside the container which is designated internally as "Video#2". In such cases the above command will also return values relating to the JPEG image producing something like this;


When this happens my script breaks. The workaround for that is to pipe the results through some unix tools to massage the output;

mediainfo --Inform="Video;%DisplayAspectRatio%,%Height%,%Format%\n" "${_TARGET}" | xargs | awk '{print $1;}'

Things to note in the revised command. There is a carriage return ("\n") at the end of the --Inform parameters which will put the unwanted data on a new line like this;


xargs will remove that line feed and replace it with a space;

1.85,720p,AVC 1.85,720p,JPEG

And finally awk will produce only the first "word" (space delimited) from the result, which produces the desired output.


Now obviously this method assumes that the first video stream in the container is the one we are interested in. I'm struggling to imagine a scenario where this would not be the case so at this point I am OK with that. If I find a file that doesn't work I might have to revise my script, but for now I will stick with this solution.

Saturday, 26 August 2017

Virtualbox remote desktop

I just had a frustrating couple of hours trying to get remote desktop working for a Virtualbox guest.

First, even though the settings screen implies that you merely need to turn remote support on you must also have the virtualbox extension pack installed.

Secondly, if you get "connection refused" or similar errors from the rdesktop client then you are probably using virtualbox 5.0.40

It wasn't until I upgraded virtualbox to 5.1.16 that it just magically started working. grrr

Friday, 21 July 2017

Booting Windows as either dual-boot physical machine or as a Virtual machine

How to boot Windows as either dual-boot physical machine or as a Virtual machine

Here is a scenario.

You have a Linux PC that you want to also dual boot to Windows. That's not hard to do right?

Unfortunately though, we all know dual booting is a bit of a pain when you just want to do something quick in Windows. You need to close everything you are doing in Linux just to boot into Windows.

One solution to that is to run Windows in a VM, that's been possible for years now right? Well the problem with that is that sometimes you need to run native Windows to say, play a 3D game.

You could maintain 2 Windows systems, one via dual-booting and the other as a VM but who wants to maintain two copies of Windows?

This is what I do.

Our starting point is a Linux system on one disk (/dev/sda). We will be installing Windows on to a separate disk that is currently empty (/dev/sdb)

WARNING: If you muck this up you can destroy all the data on your Linux system. Make sure you have backups of everything and you are abso-fricking-lutely sure you have identified the correct drive devices

You can check your disks using this command:
sudo fdisk -l
For the remainder of this tutorial I will be using /dev/sdb for the drive that will host Windows 7.

Let's get started!

In your Linux installation you want to add your user to the "disk" group:
sudo usermod -a -G disk brettg
This allows your user to access the physical drive that Windows 7 is installed on.

Note: You will need to logoff and log back in again for this change to take effect.

Install Virtualbox:
sudo apt install virtualbox
Create a place for your Virtualbox disk images:
mkdir -p $HOME/VirtualboxImages/
Create a new virtual disk that references the physical drive that Windows 7 will be installed on:
VBoxManage internalcommands createrawvmdk -filename $HOME/VirtualboxImages/Windows7.vmdk" -rawdisk /dev/sdb
Open up Virtualbox and create a new virtual machine selecting "Use an existing virtual harddisk file" when you are setting it up.

Insert your Windows CD into the virtual machine (either as a physical CD or an ISO image).

Start the VM and go through the normal Windows installation process, then log into Windows.

Open the registry editor. Edit the following keys and set them all to 0:
This forces Windows to install and load three types of disk drivers at boot. (I don't know why you need to set these to zero). By default it just installs the driver that was needed at install time. This is requireed because when we try and boot Windows later it will not be able to read the disk because it doesn't have the proper driver for it.

Shutdown the VM

You will need to add your Windows disk to grub:
sudo update-grub
Now, hopefully if everything went according to plan you should be able to reboot and find Windows listed in your grub menu. Select that and boot into Windows.

Once you are in Windows, you will have to do all the usual driver installs etc but you already knew that right?

Have fun!

Note: Tested with Ubuntu 16.04.1 host and Windows 7/10 guests

Tuesday, 24 January 2017

Using H.265 (HEVC) on Ubuntu

If you google search how to install H.265 on ubuntu you get a a bunch of posts that describe how to add a PPA for the necessary files.

However the repository hasn't been updated since 2015 (vivid vervet)

If you try to use the vivid repo then things fail because of dependency issues.

But not to worry as it seems that H.265 is now included in the standard xenial repository.

apt-cache search x265
libx265-79 - H.265/HEVC video stream encoder (shared library)
libx265-dev - H.265/HEVC video stream encoder (development files)
libx265-doc - H.265/HEVC video stream encoder (documentation)
x265 - H.265/HEVC video stream encoder

So, all you need to do is;

sudo apt-get install x265

and you are good to go.