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RealMedia
History | Clip Delivery Overview
For obvious reasons, the format of choice for Helix Universal Server is RealMedia (RealVideo and RealAudio). In practice, it is a fairly simple process to stream a RealVideo file from the server. Meta files are used, but they are only one line of code: the URL for the stream, and that’s it. So all that is needed to do is open up a text editor, specify the URL on the first and only line in the text file, and then save it with a .ram file extension instead of a .txt file extension. For a very good reference on how to do this consult the following URL:
http://www.mediacollege.com/video/format/real-media/streaming/
Note: the above reference just illustrates how to create a metafile. If you notice in the reference above, the metafile uses HTTP as the protocol to 'stream' the file. This method doesn't rely on any special streaming technology. While technically the example file is being streamed, the Helix Universal Server is left out of the mix. In this case RTSP should be used in the streaming URL as shown here:
If there’s a downside to RealMedia is that it is a one-way street once a media file is encoded to RealMedia format. Once it’s there it is virtually impossible for the end user to decode and re-edit it. This is actually quite attractive for a number of reasons. The first and foremost is that the RealVideo format offers an excellent codec that preserves just about all aspects of a video or audio stream. The second being that the file format maintains a 'copyrighted' status since it can't be easily decoded by non RealNetworks technology. Lastly but not least of all is that it does all this to the file while at the same time reducing its size, thus making it attractive for all methods of delivery: download, progressive download, and then of course streaming using streaming technology such as the Helix Server.
To deliver the streaming clips, a web site author needs only to link to RealMedia Meta files (.ram files) as though they were linking to another web page or web site. If a corporate firewall is in place at the end-user level, it is recommended to employ HTTP-cloaking, where the URL to the stream uses HTTP instead of RTSP. The difference in these URLs is as follows:
http://<server-host>/ramgen<mount-point><path>
This of course, looks like a regular URL for web sites. It is very similar to the RTSP URL’s seen earlier and it is for the most part. The only difference is the /ramgen/ specification in the URL. This is the HTTP cloaking module for RealMedia, and it allows for RealMedia streams to be accessed via RTSP through HTTP as though it were a regular web browser accessing a web page. Even though it looks like it is being progressively downloaded, the file never gets saved to the users’ computer, thereby protecting the streaming nature of the media clip.
Oddly enough, on the Windows platform the RealPlayer software supports Windows Media streams as well, and in rare cases, QuickTime streams. It can also handle flavors of MPEG, as well as Flash 4 animations, MP3 audio files and special RealPlayer-only files such as RealText, and RealPix. Most of these RealPlayer-only files are support files for what is known as a SMIL file or Synchronized Multimedia Integration Language file. This is a specially-authored file that combines audio, video, and text into a rich presentation. These presentations can be very complex to author and is beyond the scope of this document, but if more information is needed, consult the following URL: http://www.realnetworks.com/resources/howto/smil/
Embedding RealMedia in Web Pages
Again, embedding media players in web pages is generally not recommended due to web browser compatibility and usability issues, but it can be done if it must be done. In the latest releases of RealPlayer, the player can be detached from the web browser and the video can be blown up to full screen for a Television-like experience. A full reference for the code to do this can be seen by visiting:
http://service.real.com/help/ library/guides/realone/ProductionGuide/HTML/htmfiles/embed.htmClip Delivery for Windows Media | Clip Delivery for QuickTime |Other Formats