Running the QT5 Cinematic Experience Example on Raspberry Pi

I first saw the QT5 Cinematic Experience video here: 

• http://www.youtube.com/watch?v=wulbR2R1GpM

The video show cased Raspberry Pi running a very fancy QT5 example. I decided I wanted to give this a try on my Pi as well. Unfortunately it was not very straightforward. If you tried to google for instruction on run QT5 on the Raspberry Pi, it'll take you in circles. 

• http://qt-project.org/wiki/RaspberryPi_Beginners_guide
• This instruction assumes you have a main Linux machine that can be used for cross compiling.
• http://qt-project.org/forums/viewthread/21080
• This instruction asks you to download the snapshot. However the location no longer exists. 
• I also tried to use cross-ng to compile my own cross compiler. 
• Before the cross compiler finishes compiling, I found an existing cross compiler for the Pi. 
• I then checked out the Qt5 source and tried to compile that using  the cross compiler I downloaded without success.

Took me a couple nights before I figured out exactly what I need to do (turned out to be very simple). Someone backed up a copy of the Qt5 snapshot, and we can simply install from there instead of attempting to build your own cross compiler, cross compiling in Cygwin or Linux, and such. The information came from mainly the following two sources. 

• http://www.raspberrypi.org/phpBB3/viewtopic.php?f=66&t=15861&p=299166&hilit=qt5#p299166
• http://quitcoding.com/?page=work#cinex

The following outlines the steps I took to get the QT5 Cinematic Experience demo running:

1. On the Pi: sudo vi /etc/apt/sources.list
2. Append: deb http://twolife.be/raspbian/ wheezy main
3. Exit vi
4. Issue: sudo apt-get update
5. Issue: sudo apt-get upgrade // this will take a while. More than an hour for me. 
6. Issue: sudo apt-get install libqt5-* // this installs all libqt5 libraries
7. Download the Cinematic Experience source here: http://quitcoding.com/?page=work#cinex
8. Unzip the source into a folder of your liking. 
9. Navigate into your unzipped directory. 
10. Issue: qmake // this will generate the make file 
11. Issue: make // compile
12. Issue: ./Qt5_CinematicExperience // run!

Raspberry Pi: Programming with ALSA

As covered in a previous article, Raspberry Pi can be used to capture and playback audio using a USB sound card. One can do the capture using ALSA utility aplay and arecord, or programmatically using the ALSA API. 

Example recording can be found in list 4 here: 
http://www.linuxjournal.com/article/6735?page=0,2

To accommodate for my setup, I had to: 

1. Change the hardware from "default" to "plughw:0,0" in snd_pcm_open(). 
2. I also replaced the write() with an fwrite() to output to a file. 

To install the relevant headers, I had to install the following package: 

sudo apt-get install libasound2-dev

Finally, to do the compile, don't forget to link to the ALSA library using the -l option: 
gcc record.c -lasound

The example code performs the capture at 44100Hz, signed 16 bit, 2 channels, and output to simple raw format without any file headers. To verify the recording, I had to specify all the parameters using aplay: 
aplay -f s16_le -r 44100 -c 2 test.out

Raspberry Pi Remote Camera Proof of Concept Implementation

As discussed before, the Raspberry Pi has a hardware accelerated H264 encoder and decoder. This allows us to build a remote camera solution. Given that the camera module has not been released, I faked the camera input using an rolling frame buffer.

Implementation can be seen here:
http://www.youtube.com/watch?v=5ac3nU-B4WQ

Implementation details:

• 720p @ 30fps 
• UDP transport

The end result is actually quite smooth. Clearly this example can be further extended into video conference application and such. 

Raspberry Pi recording/playback with Sound Blaster Play

Raspberry Pi doesn't come with an andio in jack. Audio in can only be supported using external USB sound card. I bought a Sound Blaster Play for this purpose. 

To enable USB audio output: 
sudo vi /etc/modprobe.d/alsa-base.conf

And comment out line: 
# options snd-usb-audio index=-2

This will enable USB audio output by default. Reboot now: 
sudo reboot

Now to record: 
arecord -D plughw:0,0 -f cd test.wav

To playback: 
aplay test.wav

Note that when recording using a non-standard format: 
arecord -D plughw:0,0 -f s16_le -r 8000 -c 1 -t raw test.raw

Don't forget to insert the -D plughw:0,0 option to force data translation: 
aplay -D plughw:0,0 -f s16_le -r 8000 -c 1 -t raw test.raw