[haiku-development] Re: GSoC for MediaKit
- From: Stephan Aßmus <superstippi@xxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Fri, 20 Mar 2009 17:33:38 +0100
chao chen schrieb:
Hi,
You said that," The Haiku implementation defines an API for writing
Reader and Decoder plugins:". Can you show me some subclasses?
They are all in src/add-ons/media/plugins/ For example:
<http://dev.haiku-os.org/browser/haiku/trunk/src/add-ons/media/plugins/avcodec>
And you said "you should read enough in the BeBook documentation to
get an overview of the client API that is related to decoding and
encoding media files. Next, you should try to become familiar with the
flow of the code between libmedia.so, media_server and
media_addon_server." You mean that there are client-server structure.
In some respects, in some not. For Media Nodes, it is more like a
client/server structure, where the media_server mainly manages
cross-application communication, shared memory, notifications, and stuff
like that. For encoding/decoding, the server only keeps track of what
plugins there are and which formats they decode/encode. What I mean by
"client application" is just "an application which uses the Media Kit
API", ie libmedia.so and it's C++ classes. So for decoding, the C++ code
in libmedia.so does communicate with the media_server and
media_addon_server, but only to get an entry_ref (something like a file
handle information) to the right plugin. Then the actual plug-in loading
and object instantiation happens fully inside the client application and
the server has nothing to do with it anymore.
And is there uml diagram to show the relationship among classes?
Unfortunately no, I don't believe so.
The
client has encoder and decoder. I want to know where the ReaderPlugin.h
DecodePlugin.h EncoderPlugin.h should be used?
See above, it's used only in those plugins, and some libmedia.so classes
that directly deal with those plugins. I don't know off-hand which ones.
But it should be easy to grep the code to get a first overview.
Is the work stream like:
media_addon_server is like a backend service and montor the folder. If
someone puts a new plugin in the folder, the media_addon_server will
update its formats. Then client application starts, requests the
information from media_server, and media_server gets the format from the
media_addon_server, then media_server encode or decode the media and
send the information to client?
For the most part, this is correct. The format for the current file is
somehow constructed, I have forgotten how that is done. I don't remember
if each decoder plugin is given a chance to identify the file, or if the
format is constructed another way. I believe it's done another way and
only those plugins get to look a the file which are potential
candidates. (David/Marcus please correct me, if I am wrong.)
Anyways, the decoding the happens fully in the application, the servers
are not involved in that anymore.
I didn't think clearly about this yellow part. Because the client has
its encoder and decoder, the media_server only send the format to the
client?
The client sends the format, the server tells it what plugin to use. You
definitely need to look at the src/kits/media code to get the full
picture and the most precise information.
Best regards,
-Stephan
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