A Recap of Fixing Bug ID 680484

Recently I have fixed the bug 680484 and learned a lot from the process. Therefore I think it deserves a blog post to share my story. The bug 680484 is about a crash when running the program gupnp-dlna-info to dump the input media file’s metadata with -v option. This crash only happens to gupnp-dlna-info linked against gstreamer-1.0. Gstreamer is a comprehensive multimedia processing library. gupnp-dlna, and many other GNOME multimedia packages, depends on it to deal with media files. Nowadays Gstreamer is under the flux from 0.10 to 1.0 (or 0.11) and many GNOME programs are busy with migrating to the Gstreamer-1.0 APIs.

A good introduction to gstreamer-1.0 can be found here. The link also provides the PPA links to install 1.0 on Precise. However I found that the APIs in this PPA slightly fall behind the head of the git. (Update: as of today, Aug 11, 2012, the PPA version is good) So I would recommend to use JhBuild to install the master version of Gstreamer by running jhbuild build gstreamer-master. You probably also need to build gst-plugins-good-master, gst-plugins-bad-master and gst-plugins-poor-master to install the necessary plugins.

To fix the bug 680484 I first verified gupnp-dlna-info had linked to the correct version of gstreamer.

[riko@localhost] tools $ ./gupnp-dlna-info --gst-version
GStreamer Core Library version

Now I reproduced the crash by issuing the command like this

[riko@localhost] tools $ ./gupnp-dlna-info ../../../gupnp-dlna-media/strict/audio/NiN_Ghosts_IV_34.mp3 -v

Profile Name: (null)
Profile MIME: (null)

  audio: audio/mpeg, mpegversion=(int)1, mpegaudioversion=(int)1, layer=(int)3, rate=(int)44100,
  channels=(int)2, parsed=(boolean)true
  Segmentation fault

To make the debugging easier I compiled the gupnp-dlna-info with shared build disabled and ‘-g’ flags to CFLAGS

[riko@localhost] gupnp-dlna $ ../../gupnp-dlna/configure --enable-shared=no CFLAGS='-g'

Next I used cgdb to load the program

cgdb --args ./gupnp-dlna-info ../../../gupnp-dlna-media/strict/audio/NiN_Ghosts_II_12_lo.mp3 -v 

In cgdb debugging window I ran the program to make it crash

Now use the command backtrace or bt to retrospect the flow of function calls.

By analyzing the function call history I decided to move the history backwards 4 steps and found a suspicious call.

After referring to the gstreamer-0.10 to 1.0 migration guide, I figured out that the line gst_structure_to_string ((GstStructure *) taglist) was deprecated and I should use gst_tag_list_to_string (taglist) instead. So I verified that in gdb and it seemed to work.

It turned out that was the reason for the crash. Fixed it and the crash was gone.

How to use Rygel to share video and play it back in Totem

In my first OPW progress report I mentioned that I used XBMC player to play back the multimedia files by Rygel. Zeeshan asked if I could use a GNOME DLNA player. Actually I had tried Totem player with Coherence plugin but failed. In the age of GNOME 3, the Coherence plugin is probably obsolete and doesn’t work anymore (no wonder that Totem plugin package in Ubuntu 12.04 didn’t include the Coherence plugin). That was the reason I switched to use non-GNOME apps like XBMC and eezUPnP. But recently I found out there is a GNOME project Grilo that can make Totem work. And I had a feeling that Grilo is gonna replace Coherence as the primary UPnP plugin for Totem. By checking out the git source of Totem, under the plugins directory, there is no more coherence_upnp. Grilo plugin first appeared in Totem 3.2.0 which means that you probably can’t install Grilo plugin for Totem by running ‘apt install’ in Ubuntu 12.04. Therefore I downloaded the latest source release of Totem (3.4.3), compiled and installed it. It ran great on my machine. The following screenshot shows how it looks like:

Use Grilo plugin for Totem to browse the media files shared through Rygel