[haiku-development] Re: GSoC for MediaKit
- From: chao chen <chillycreator@xxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Sat, 21 Mar 2009 00:05:26 +0800
Hi,
You said that," The Haiku implementation defines an API for writing
Reader and Decoder plugins:". Can you show me some subclasses?
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. And is there uml diagram to show the
relationship among classes? The client has encoder and decoder. I want to
know where the ReaderPlugin.h DecodePlugin.h EncoderPlugin.h should be used?
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?
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?
Thanks!
-chico
2009/3/20 Stephan Assmus <superstippi@xxxxxx>
> Hi Chico,
>
> > I am a student from Graduate University of Chinese Academy of
> Sciences.
> > My major is basic software. I love to know the detail of how the os and
> > other software works. I have got an IBM certificate of linux in 2008. And
> > I
> > have developing experience on windows platform. I like to use c and java,
> > especially c++ to programming. During 2007-2008, I was an intern of
> > SDET(Software Develop Engineer in Test) in Microsoft ATC, and I also got
> > choice to be a SDET FTE. I had developed Mini DBMS using c++ during my
> > university life, and my job was designing and coding DBMS kernal and
> basic
> > structures. I perfer to do some work in MediaKit, although I didn't have
> > much experience in media programming and haiku os. It's a chanllege for
> > me,
> > and I love to know more.
> > Do you have any suggestions? Let me know. Thanks.
>
> First of all, thank you for your interest in Haiku! Do you have Haiku
> already running in some form? Real hardware, some virtual machine?
>
> To give you an overview: The MediaKit is composed of a client API (defined
> by BeOS) and the backend, which partly happens in the communication between
> several applications (client application communicates to media_server and
> media_addon_server). The main entry points for encoding media is through the
> BMediaFile and BMediaTrack API classes. These roughly correspond to managing
> container formats (AVI, MKV, MOV, ...) and codecs for media streams (RAW,
> XVID, MJPEG, ...). To get a good overview of the MediaKit C++ class
> framework, I suggest consuming the relevant parts of the BeBook developer
> documentation:
>
> <http://www.haiku-os.org/legacy-docs/bebook/TheMediaKit_Overview.html>
>
> and
>
> <http://www.haiku-os.org/legacy-docs/bebook/TheMediaKit.html>
>
> Of the class documentation, see especially
>
> <http://www.haiku-os.org/legacy-docs/bebook/TheMediaKit_Functions.html>
> <http://www.haiku-os.org/legacy-docs/bebook/BMediaFile.html>
> <http://www.haiku-os.org/legacy-docs/bebook/BMediaTrack.html>
>
> This is the API for which the backend needs to be implemented. Now, the
> important part to understand is that *decoding* media already has the
> implementation in the backend. The API to implementing media codecs on BeOS
> has always been private and only selected developers have received the
> documentation for implementing new plugins. The Haiku implementation defines
> an API for writing Reader and Decoder plugins:
>
> <
> http://dev.haiku-os.org/browser/haiku/trunk/headers/private/media/MediaPlugin.h
> >
> <
> http://dev.haiku-os.org/browser/haiku/trunk/headers/private/media/ReaderPlugin.h
> >
> <
> http://dev.haiku-os.org/browser/haiku/trunk/headers/private/media/DecoderPlugin.h
> >
>
> First of all, 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. What happens when
> a client application instantiates a BMediaFile, iterates over it's tracks to
> instantiate BMediaTrack objects and finally uses those to decode media
> buffers? A similar thing needs to happen for encoding, so first you need to
> be familiar to how things are done in decoding. An important thing to
> understand here is that the media_addon_server maintains a mapping of all
> known "media_format" definitions to plugins which implement decoding the
> respective format. It will try to keep the mapping up to date, ie when the
> user drops a new plugin in the right folder, the list of known formats and
> the mapping is updated (lazily). When a client application then requests
> decoding a certain format, t
> he media_addon_server will scan through it's list of known formats and
> find a respective plugin. The entry_ref for this plugin is passed back to
> the client application and is then used to open the plugin and instantiate
> the respective C++ objects in the backend.
>
>
> In parallel to this, you should try to become familiar with our coding
> guide lines (which you will need to follow strictly), and you should try to
> get everything ready in terms of development environment, becoming familiar
> with our source tree structure... and such stuff. :-) For this we have
> various "getting started" type of documentation on our website.
>
> Should have any questions, please don't hesitate to ask! :-) Also, please
> keep in mind that you may very well present better ideas for implementing
> the MediaKit backend. Specifically, I would personally welcome ideas that
> make it easier for Haiku to stay up-to-date with other open source media
> projects, if that is somehow possible. Regard the code you need to write for
> this project as a kind of "putting things together" type of work. Existing
> things -- on one hand the existing Be Media Kit API and on the other hand
> existing codec implementations, like those in the ffmpeg project -- need to
> be put together in an elegant and extensible way.
>
> Best regards,
> -Stephan
>
>
>
>
>
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