Software Lab

Software experiments. Mostly open source.

Pulseaudio device names

by

Recording audio with gstreamer is easy:

  gst-launch -e pulsesrc ! audioconvert ! \
    lamemp3enc target=1 bitrate=64 cbr=true ! \
    filesink location=audio.mp3

The pulsesrc element here refers to the pulseaudio input (pulseaudio is AFAIK the default sound system in all linux distributions nowadays). This is good and will capture audio from the default sound input, which can be microphone or line-in depending on the hardware and the pulseaudio configuration.

But what if I plug in my USB webcam with built-in microphone and I want to capture audio from that?

Read more

Satellite Tooltips

by

Satllite tooltip in GpredictYou may have already seen tooltips in the Gpredict user interface. I have made extensive use of them for providing short description of the functionality of the GUI controls all over the application. Lately, I have felt a desire to extend the usage of tooltips to also include graphical objects like satellites shown on the map or the passes shown in the “Sky at a glance” module.

Gpredict uses GooCanvas for graphics, which adds a the “missing” 2D canvas library to Gtk+. Since version 0.15 GooCanvas includes support for Gtk+-like tooltips for any objects on the canvas. This is really great since it simplifies the effort from messing with own popup windows to using single line API calls.

Read more

Gstreamer compositing using the GstvideoMixerPad properties

by

Few weeks agio I posted my notes about picture-in-picture compositing in Gstreamer using nothing else than the gst-launch command line tool. I also wrote that I could not figure out how to use the xpos, ypos, zorder properties of the GstVideoMixerPad element. I got a comment on this note from Jan Schmidt telling that these properties can not be used with gst-launch but are easily accessible from Python. He also gave a very cool example that shows how to use it.

Read more

Ubuntu Linux on the Acer Aspire 5745G Laptop

by

–

Info icon This article is about running Ubuntu Linux 10.04 on the Acer Aspire 5745G. If you are interested in running Ubuntu 10.10 check this article instead.

It was time for me to get a new computer and this time I was going for laptop with a fast CPU and sufficient Nvidia graphics that is suitable for video processing and high bandwidth software defined radios. Didn’t want ATI graphics because I have bad experience with ATI and Linux. Nvidia on the other hand has been working very well for me on Linux.

I thought of getting a new Macbook Pro 15″ with and Intel i7 dual core processor, but I ended with the Acer Aspire 5745G-724G50Mn with an i7 quad-core, 4GB RAM and a Geforce GT330M with 1 GB VRAM. The rest of this article describes my first experiences with installing and running Ubuntu Linux 10.04 Lucid Lynx 64 bit on this computer side by side with the pre-installed Windows 7.

Read more

More GStreamer Tips: Picture-in-Picture Compositing

by

In a previous post I gave a few examples showing how simple text overlays can be added to any video stream in GStreamer. Now it’s time to look at compositing between two or more video streams, also called picture in picture. As you’ll see it is still very easy to achieve even when using nothing more than the gst-launch command line tool. First we look at some basic examples, then we finish with a more complex “Live from Pluto” video wall.

Read more

Simple time-lapse video with gtreamer and ffmpeg

by

I have experienced an unexpected spin-off while fooling around with GStreamer and my Logitech QuickCam Vision Pro 9000 webcam: A simple and easy way to autonomously capture and render time-lapse videos.

One of the advantages of webcams compared to other digital still and video cameras is that it can be controlled from a computer and the captured frames are transfered from the camera to the computer in real-time using the USB interface. This is pretty much the definition of a webcam and this feature is indeed very convenient for capturing time-lapse videos. Unfortunately, the image quality of webcams has not been anywhere near good enough to make nice looking time-lapse videos but this has changed over the last few years and is continuously improving. The results presented in this article are captured using my Logitech QuickCam Vision Pro 9000 – one of the greatest UVC cameras out there.

Read more

A Weekend with GStreamer

by

Gstreamer LogoThis weekend was dedicated to learning and experimenting with Gstreamer – an open source library and framework for constructing audio and video processing pipelines. Despite the weekend being spoiled by lots of bad luck (power outages, Internet down, etc.) I managed to beat the hell out of Murphy and get some work done!

My hidden agenda is of course finding a good audio/video library to accompany a software defined radio created using GNU Radio and the Universal Software Radio Peripheral (USRP), and to eventually be able to transmit real time high definition video over the air. While GNU Radio and the USRP can take care of everything related to software radio and RF, I am still looking for a good framework for flexible audio/video processing.

Read more

Ubuntu 9.04 on the Eee PC 701

by

It’s been more than a year now that I last posted an update about using my Asus Eee PC 701 for hamradio. To be honest, my Eee PC has been more or less idle ever since. Back in August 2008 I have decided that I need a newer and better OS on it than the Asus/Xandros that it came installed with. I tried a few one every now and then but without any satisfactory results. Until now…

Read more