Tuesday, May 06, 2008

Elisa problems marshalling MediaUri

The short version
If you are having problems with elisa not playing your local media files (see https://code.fluendo.com/elisa/trac/ticket/957 and https://code.fluendo.com/elisa/trac/ticket/961) then you can fix it by editing ~/.elisa/elisa.conf and changing gstreamer:gst_metadata_client to gstreamer:gst_metadata. That is all and it works!

The long version
Ever since I heard about elisa, I have been trying to get it to work as my media center. It was well designed and the vector graphics are awesome. It plays music, videos and displays pictures, and has several plug-ins to play online music and youtube videos etc. You can even get cover arts from amazon from with in the software. But there is just one problem. It could never play my local media. Neither movies, nor music and not even photos. I gave v0.3.3 of elisa a try. It did not play my personal media. I thought, well it is still in development, so why not wait for the next release. I did not even take a look at the logs.

Then came v0.3.4 and that again did not work. So I synced up to the latest code in svn and tried that. No luck. At this point I was starting to think something must be wrong with my configuration or the versions of dependencies that I have installed. This time I looked at the logs and a warning pointed me to a log file in /tmp. A quick look and I could not understand why jelly.py (from twisted) seems to think MediaUri is not a known type. I didn't know much about twisted framework (and I still don't), so I emailed the elisa mailing list. And in response a developer kindly opened a ticket for me. You can view it here https://code.fluendo.com/elisa/trac/ticket/961.

I was waiting for it to get fixed. And then along came the announcement for v0.3.5. I decided to try the latest from source control and it failed to play my media again. This time I was adamant on learning twisted at least up to the point of understanding what jelly.py is and why it is does not know the type of MediaUri. I found out that jelly is used to serialize data to send it over the wire to the server to unmarshall and act on it. That is good enough. Now back to the exception
Traceback (most recent call last):
File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 182, in addCallbacks
self._runCallbacks()
File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 307, in _runCallbacks
self.result = callback(self.result, *args, **kw)
File "/home/chandanp/workspace/python/fluendo/elisa/elisa-plugins/elisa/plugins/gstreamer_plugin/gst_metadata.py", line 1429, in got_root
dfr = root.callRemote('get_metadata', dic, low_priority)
File "/usr/lib/python2.5/site-packages/twisted/spread/pb.py", line 380, in callRemote
_name, args, kw)
--- <exception caught here> ---
File "/usr/lib/python2.5/site-packages/twisted/spread/pb.py", line 853, in _sendMessage
netArgs = self.serialize(args, perspective=perspective, method=message)
File "/usr/lib/python2.5/site-packages/twisted/spread/pb.py", line 807, in serialize
return jelly(object, self.security, None, self)
File "/usr/lib/python2.5/site-packages/twisted/spread/jelly.py", line 879, in jelly
return _Jellier(taster, persistentStore, invoker).jelly(object)
File "/usr/lib/python2.5/site-packages/twisted/spread/jelly.py", line 464, in jelly
sxp.append(self.jelly(item))
File "/usr/lib/python2.5/site-packages/twisted/spread/jelly.py", line 468, in jelly
sxp.append([self.jelly(key), self.jelly(val)])
File "/usr/lib/python2.5/site-packages/twisted/spread/jelly.py", line 489, in jelly
raise NotImplementedError("Don't know the type: %s" % objType)
<type 'exceptions.NotImplementedError'>: Don't know the type: <class 'elisa.core.media_uri.MediaUri'>

This simply means that there is a problem serializing MediaUri. I greped around and found that MediaUri is not extending one of the serializable classes. So that could be the problem. I looked at the gst_metadata.py which is where the RPC is being made. I noticed that there is another way to get metadata, but it is not an asynchronous call. But hey what the heck, I don't care if the UI locks up for a while when it is scanning my media as long as I can get it to work. So if I used gst_metadata instead of gst_metadata_client I can get away from the whole async RPC calls. I edited ~/.elisa/elisa.conf and changed gstreamer:gst_metadata_client to gstreamer:gst_metadata and guess what, it works!

I updated a ticket with the same problem I was having and at least some one is happy being able to play their local media. The link to the ticket is https://code.fluendo.com/elisa/trac/ticket/957. I got so excited that I wrote this blog immediately. Now I will take elisa for a ride.
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