Switching Raspbian to Pixel desktop

Official Raspbian images based on Debian Stretch by default has the Pixel desktop environment and will login new users to it. But if you have had a Raspbian installation with another DE (such as LXDE), here are the steps to install and login to the Pixel desktop.

  1. apt-get install raspberrypi-ui-mods
  2. sed -i 's/^autologin-user=pi/#autologin-user=pi/' /etc/lightdm/lightdm.conf
  3. update-alternatives --set x-session-manager /usr/bin/startlxde-pi
  4. sed -i 's/^Session=.*/Session=lightdm-xsession/' ${USER}/.dmrc

Make sure the user’s ‘.dmrc’ file is updated with the new startlxde-pi session as that is where lightdm login manager looks to decide which desktop should be launched.


Improvement in converting video/audio files with VLC

VLC Media Player has the ability to convert video/audio files into various formats it supports, since a long time. There is a dedicated “Convert/Save” menu for converting single or multiple files at once into a different format, with limited ‘editing’ features such as specifying a start time, caching options etc. It is quite useful for basic editing/cropping of multimedia files.

As an example, one of the easiest ways to create a custom iPhone ringtone is to create a “.m4r” (AAC format) file exactly 40 seconds long. It is a matter of selecting your favourite music file and doing a “Convert/Save” with appropriate “Profile”. A “Profile” specifies the video/audio encoding to be used, which can be easily customized by selecting different audio and video codecs.

The options “Caching time”, “Play another media synchronously” (think adding different sound track to a video clipping) and a “Start time” etc can be specified under “Show more options” button and even more advanced functionality is available by making use of the “Edit Options” line. Internally, all the options specified at this line are passed to the converter.

There was one thing lacking in this “Convert/Save” dialog though – there was no possibility to specify a “Stop Time” akin to the “Start Time”, in the GUI (although it can be manually specified in the “Edit Options”, but you need to calculate the time in milliseconds). VLC 2.x series convert looks like as follows – notice the lack of “Stop time”:


Being bugged by this minor annoyance, I set out to add the missing “Stop-time” functionality. Going through the codebase of VLC, it was relieving to see that the converter backend already supports “:stop-time=” option (akin to “:start-time=”). It was then a matter of adding “Stop Time” to the GUI and properly updating the “Edit Options” when user changes the value.

A working patch was then sent to vlc-devel mailing list for review and feedback. After 5 rounds of review and constructive feedback from Filip Roséen the code was cleaned up (including existing code) which is now committed to the master branch. This functionality should be available to users in the upcoming 3.0 release. Screenshot below:



Convert iPhone contacts to vCard

On a recent troubleshooting attempt, I lost all the contacts in my Android phone. It had also received a recent update which took away the option to import contacts from another phone via bluetooth.
I still had some contacts in the old iPhone, but now that mass transfer via bluetooth is gone, it was a question of manually sending each contact in vCard format to the Android phone. That means I should probably find a less dreadful way to get the contacts back.

Here is one way to extract contacts en-masse from iPhone into popular vCard format. The contact and address details in iOS are stored by AddressBook application in a file named ‘AddressBook.sqlitedb’ which is an sqlite database. The idea is to open this database using sqlite, extract the details from a couple of tables and convert the entries into vCard format.

Disclaimer: the iPhone is an old 3GS running iOS 6 and it is jailbroken. If you attempt this, your mileage would vary. Required tools/softwares are usbmuxd (especially libusbmuxd-utils) and sqlite, with the prerequisite that openssh server is running on the jailbroken iPhone.

  1. Connect iPhone via USB cable to the Linux machine. Run iproxy 2222 22 to connect to the openssh server running on the jailbroken phone. iproxy comes with libusbmuxd-utils package.
  2. Copy the addressbook sqlite database from phone:scp -P 2222 mobile@localhost:/var/mobile/Library/AddressBook/AddressBook.sqlitedb .Instead of steps 1 and 2 above, it might be possible to copy this file using Nautilus (gvfs-afc) or Dolphin (kio_afc) file manager, although I’m not sure if the file is accessible.
  3. Extract the contact and address details from the sqlite db (based on this forum post):sqlite3 -cmd ".out contacts.txt" AddressBook.sqlitedb "select ABPerson.prefix, ABPerson.first,ABPerson.last,ABPerson.organization, c.value as MobilePhone, h.val ue as HomePhone, he.value as HomeEmail, w.value as WorkPhone, we.value as WorkEmail,ABPerson.note from ABPerson left outer join ABMultiValue c on c.record_id = ABPerson.ROWID and c.label = 1 and c.property= 3 left outer join ABMultiValue h on h.record_id = ABPerson.ROWID and h.label = 2 and h.property = 3 left outer join ABMultiValue he on he.record_id = ABPerson.ROWID and he.label = 2 and he.property = 4 left outer join ABMultiValue w on w.record_id = ABPerson.ROWID and w.label = 4 and w.property = 3 left outer join ABMultiValue we on we.record_id = ABPerson.ROWID and we.label = 4 and we.property = 4;"
  4. Convert the extracted contact details to vCard format:cat contacts.txt | awk -F\| '{print "BEGIN:VCARD\nVERSION:3.0\nN:"$3";"$2";;;\nFN:"$2" "$3"\nORG:"$4"\nEMAIL;type=INTERNET;type=WORK;type=pref:" $9"\nTEL;type=CELL;type=pref:"$5"\nTEL;TYPE=HOME:"$6"\nTEL;TYPE=WORK:"$8"\nNOTE:"$9"\nEND:VCARD\n"}' > Contacts.vcf
  5. Remove the empty content lines if some contacts do not have all the different fields:sed -i '/.*:$/d' Contacts.vcf

Now simply transfer the Contact.vcf file containing all the contact details to Android phone’s storage and import contacts from there.

TeX: Justification with no hyphenation

I’ve been reading a copy of 1984 by George Orwell, published by Fingerprint publishing — a beautifully typeset one. Already into half of Part II, but that’s when I noticed that the book is typeset with full justification sans any hyphenation. Incidentally I was typesetting something else, which probably is the reason I noticed it now. And I wanted to typeset my article the same way, with full justification but no hyphenation.

Biggest strength of TeX is its line, paragraph and page breaking algorithms where hyphenation plays a big part. Thus removing hyphenation means taking away a lot of those advantages. In any case, there are seemingly multiple ways to do it. From the TeX FAQ:

Use hyphenat package with


or set \hyphenpenalty and \exhyphenpenalty to 10000. These avoided hyphenation, but justification was bad – there were long words extending beyond the right margin. So moved on to next solution:


This one kept hyphenation to the minimum with justified text, but didn’t fully avoid it. And it would work only for text with current font. \sloppy sets \tolerance and \emergencystretch to large values.

And the last one, which provided full justification with no hyphenation is:


The \tolerance parameter sets how much badness is allowed, which influence paragraph/line breaking. \emergencystretch is the magical parameter which stretches text over multiple passes to balance the spacing. Setting \hyphenpenalty to infinite value actually has better effect than setting \tolerance.

Kerning feature for Malayalam fonts

At SMC, we’ve been continuously working on improving the fonts for Malayalam – by updating to newer opentype standard (mlm2), adding new glyphs, supporting new Unicode points, fixing shaping issues, reducing complexity and the compiled font size, involving new contributors etc.

Recently, out of scratching my own itch, I decided that it is high time to fix the annoyance that combination of Virama(U+D04D ് ) with quote marks (‘ ” ‘ ’ “ ” etc) used to overlap into an ugly amalgam in all our fonts. Usually Virama(് ) connects/combines two consonants which makes all 3 into a new glyph – for example സ+്+ന is shaped into a new glyph സ്ന (Note that you need a traditional orthography font installed to see the distinction in this example. Many of them are available here) . The root of the problem is that sometimes when Virama(് ) appears individually in a word such as “സ്വപ്‌‌നം” it connects two consonants പ and ന, it is positioned above the x height of most glyphs and it shall not have much left and right bearing to avoid ugly spacing between the consonants പ and ന.  Because of small side bearings, in fact of the negative right bearing (് protrudes beyond the right bearing) when a quote mark follows it, quote mark gets a little juxtaposed into Virama glyph and renders rather bad. The issue is quite prominent when you professionally typeset a book or article in Malayalam using XeTeX or SILE.

Fontforge’s tools made it easy to write opentype lookup rules for horizontal pair kerning to allow more space between Virama(് ) and quote marks. You can see the before and after effect of the change with Rachana font in the screenshot.


Update 26/03/2016: Many applications already support the kerning feature out of the box, including Firefox, SILE and VLC (3.0.0-git for subtitles) that I have tested, but many still need support, for instance LibreOffice, Kwrite etc. Here is a screenshot of VLC (3.0.0-git) taking kerning rules into account while displaying Malayalam subtitle.


Other fonts like AnjaliOldLipi, Meera and Chilanka also got this feature and those will be available with the new release in the pipeline. I have plans to expand this further to use with post-base vowels of വ(്വ) and യ(്യ) with abundant stacked glyphs that Malayalam has.

VLC now render subtitles in South Asian scripts!

If you were following VLC development status (hey, you should follow the awesome Jean-Baptiste Kempf’s weekly updates!), you might have noticed some recent improvements on how VLC handles subtitle text rendering. In May 2015, the freetype module was improved to use Harfbuzz for text shaping. On the week of August 4, it was mentioned that the internals of VLC subtitle handling were completely rewritten . And in last week’s (October 26) update it mentioned Salah-Eddin added support for font fallback in the freetype module; which would mean that there is no need to set a specific font to display particular script/language.

All this combined, it should mean that complex text shaping and rendering for subtitles should work fine out of the box. To test this, I built the VLC 3.0.0-git master branch by checking out the code, creating a tar ball and adapting the spec file from RPMFusion to build RPM package. NOTE: don’t remove '.git*' files while creating tar ball, otherwise building would fail. Then edited/translated one of the .srt subtitle files and used that to play a movie. The result is – Malayalam subtitles are shaped and rendered beautifully!

VLC rendering Malayalam subtitle

VLC rendering Malayalam subtitle

Jean-Baptiste Kempf tells me that this should also work fine with Android (since version 1.6.90) as well as with Windows. Totem (GNOME Vidoes) have been displaying complex texts correctly since years but VLC lacked that feature till now. This is an awesome news for people who were limited in enjoying world movies in their own language. There are collectives like MSone where volunteers translate world movies’ subtitles to Malayalam and help those to reach wider audience.

Kudos to the awesome Videolan team!