Helix Universal Server is ready to stream prerecorded clips right after installation. As with any Internet server, you request content from Helix Universal Server using a hypertext URL, which you typically add to a Web page. This chapter explains link formats, introducing you to mount points. It shows you how to launch a media player from a Web page, and covers additional features that help you deliver prerecorded clips.
A Web page hyperlink to content on Helix Universal Server launches a media player and streams some content, whether a prerecorded clip or a live broadcast. A typical link to a media clip or a broadcast served by Helix Universal Server includes the server address, protocol port (optional), mount points, path, and file name:
protocol:// |
The following illustration shows the parts of a typical link. Not every link includes the same components, however.
The following table describes common link components.
| Component | Specifies |
|---|---|
protocol:// |
The protocol used to initiate streaming. This is rtsp://, mms://, pnm://, or http://. For more information on these protocols, see "Application-Layer Protocols". |
address |
Address of Helix Universal Server, either a dotted IP address or a machine and domain name. |
port |
Port where Helix Universal Server listens for requests on the specified protocol. This is not required if Helix Universal Server uses the default, well-known ports. For more on ports, see "Defining Communications Ports". |
mount_points |
One or more mount points that invoke Helix Universal Server features. You can stream simple, on-demand clips using just a forward slash after the address and port. For more information, see "Mount Points". |
path |
An optional path relative to the Content directory. If the file is in the Content directory, no path is required. Broadcast URLs do not include a path. For more information, see "Creating Content Subdirectories". |
file |
The name of the presentation, including the extension. The file can be a clip or a metafile used to launch the clip, as described in "Launching Media Players and Opening URLs". Broadcasts also use a file name specified by the encoder, even if no file is created on the computer. |
| Tip: For examples of the different types of links, as well as the features of SMIL files, view the demonstrations by clicking Server Setup>Media Samples in Helix Administrator, and then choosing the SMIL demonstration links. |
All URLs to clips or live streams served by Helix Universal Server include at
least one mount point that looks like a directory listing in the request URL. If
you worked through the section "Creating and Streaming a Clip on Demand",
you may have written a Web page URL that includes the /ramgen/ mount
point, like the following example:
<a href="http://helixserver.example.com |
In the preceding URL, the /ramgen/ mount point does not correspond to a
physical path on the Helix Universal Server computer. Instead it's a virtual
path that invokes a Helix Universal Server feature. In this case, the mount
point tells Helix Universal Server to use its Ramgen feature to send the
browser a MIME stream that launches RealOne Player.
| For More Information: For more on Ramgen, see "Using a Client Launch Utility". |
Using Ramgen launches RealOne Player and passes it the media URL. The
URL that RealOne Player uses, however, does not include the /ramgen/ mount
point, which has already served its purpose. Additionally, the URL is
reconfigured to use the RTSP streaming protocol. Hence, RealOne Player
receives the following URL for requesting the streaming content:
rtsp://helixserver.example.com/video1.rm |
This URL also contains a mount point, though it's easy to miss because it's simply the slash that precedes the clip name:
... |
This mount point indicates that the clip resides in Helix Universal Server's
main content directory. This directory, named Content, is located in the Helix
Universal Server installation directory. A directory linked to a mount point is
known as the mount point's base path. In a default installation on Windows,
the base path for the "\" mount point is the following:
C:\Program Files\Real\Helix Server\Content |
On UNIX, installation locations may differ, but the content directory falls under the main Helix Universal Server directory:
/usr/local/Real/HelixServer/Content |
The "/" mount point therefore masks the actual path to the streaming media content on the Helix Universal Server computer.
| For More Information: "Streaming Clips On Demand" contains additional information about paths and mount points for streaming on-demand clips. |
A URL may have several mount points. In the quick start section
"Broadcasting a Stream", you had the option of creating a Web page URL to
play a live broadcast, using two mount points as in the following example.
Here, the /ramgen/ mount point launches RealOne Player, whereas the
/broadcast/ mount point indicates that the content is live rather than
prerecorded:
... |
When a URL includes /broadcast/, Helix Universal Server does not search its
content directory for a clip named live.rm. Instead, it knows that the URL is to
a live stream sent by Helix Producer. The configuration information for the
/broadcast/ mount point gives Helix Universal Server the information it needs
to find the content, such as what server port Helix Producer uses to deliver the
stream.
Helix Universal Server predefines mount points for many features. You add certain mount points to URLs to insert advertisements in media clips, for example. In some cases, you need to define your own mount points to set up a feature. When a feature requires a mount point, this guide's instructions on implementing that feature explain how to configure the mount point, as well as how to add the mount point to URLs to invoke the feature. In many cases, URLs must list mount points in a specific order for the various features to work.
A clip that streams over the RTSP or MMS protocol must use a URL that
starts with rtsp:// or mms:// rather than with http://. Because browsers cannot
make RTSP or MMS requests, you cannot link a Web page directly to a
streaming media clip that uses a streaming protocol. You resolve this problem
either by adding a metafile, or using a client launch utility on Helix Universal
Server.
| Note: Most media players also have an Open command that lets viewers enter a media URL directly without clicking a link. In this case, the URL is the same as that used in a metafile. Although viewers can play clips this way, this method is not recommended because it is awkward and prone to errors. |
A metafile is a simple text file that links to a Web page through a standard <a
href> link that specifies the HTTP protocol. The metafile contains the
streaming media URL, and uses a file extension that causes the Web browser
to launch a media player as a helper application. The browser then passes the
metafile to the media player, which requests the streaming content over a
streaming protocol. Each media player uses a different type of metafile.
For RealOne Player, metafiles are known as Ram files because they use the file
extension .ram. If the media is embedded in a Web page, though, the file
extension is .rpm. When the viewer clicks the Web page link to the Ram file,
the browser launches RealOne Player and gives it the Ram file, which contains
the URL to the streaming clip, such as the following:
rtsp://helixserver.example.com/video1.rm |
RealOne Player can also play SMIL presentations that coordinate multiple clips. In these cases, the SMIL file lists the RTSP URLs to the clips. The Ram file gives the RTSP (or HTTP) URL to the SMIL file.
| For More Information: The presentation delivery chapter of RealNetworks Production Guide covers the Ram file syntax, and explains how content creators can use the Ram file to pass playback parameters to RealOne Player. |
| Tip: A Ram file feature called a cloakport switch helps you to mitigate the effect of restrictive firewalls on RTSP clients. This switch passes Helix Universal Server port information to the client in case the RTSP connection is blocked by a firewall. See "Handling Communication through Nonstandard Ports". |
Although Apple's QuickTime Player also receives streaming content over RTSP, it has its own metafile extension and syntax. You use the QuickTime MakeRefMovie tool to create a reference movie that contains the RTSP URL or URLs to your QuickTime presentation on Helix Universal Server.
| For More Information: See the QuickTime documentation for information on MakeRefMovie. You may find the Web page http://www.apple.com/quicktime/products/tutorials/ref movies.html helpful as well. |
ASX files are the Windows Media equivalent to RealNetworks Ram files. They
are plain text files that use the file extension .asx. They list the URLs to
Windows Media clips that stream over the MMS protocol. Within the ASX
file, the requested content uses an mms:// link that points to Helix Universal
Server:
mms://helixserver.example.com/video2.wmv |
| For More Information: See your Windows Media documentation for instructions about writing ASX files. The ASX file can also include information to work around restrictive firewalls. |
As an alternative to writing a metafile, you can use a client launch utility that allows you to link your Web page directly to a streaming clip. In this case, the Web page URL used to request the streaming clip must include the mount point for the launch utility. This causes Helix Universal Server to launch the appropriate media player, and stream the clip using the player's preferred streaming protocol. Helix Universal Server includes launch utilities for RealOne Player and Windows Media Player. QuickTime has no equivalent utility.
Helix Universal Server's Ramgen utility is preconfigured with a /ramgen/
mount point that launches RealOne Player. To use the Ramgen utility, you
include the /ramgen/ mount point in a Web page URL to a streaming clip, just
after the Helix Universal Server address. To enable the browser to make the
request, you use the HTTP protocol rather than RTSP:
<a href="http://helixserver.example.com/ramgen/video1.rm">Play RealMedia</a> |
When Helix Universal Server receives a request that contains the /ramgen/
mount point, it sends a MIME stream to the browser that launches RealOne
Player. It then streams the clip or SMIL file to RealOne Player using the RTSP
protocol. Hence, the preceding Ramgen link is equivalent to linking to a Ram
file from a Web page:
<a href="http://www.example.com/launch_video.ram">Play RealMedia</a> |
and having the launch_video.ram file request the clip over RTSP:
rtsp://helixserver.example.com/video1.rm |
| Note: To circumvent restrictive firewalls, Helix Universal Server adds the cloakport switch when using Ramgen. For more information, see "Handling Communication through Nonstandard Ports". |
| For More Information: Content creators can learn about Ramgen from the presentation delivery chapter of RealNetworks Production Guide. Note that Ramgen does not support as many playback parameters as a Ram file, which makes the Ram file a more powerful tool for content creators. |
ASXGen is the equivalent to Ramgen for launching Windows Media Player.
Helix Universal Server comes configured with a mount point named /asxgen/,
which you add to a Web page link instead of writing an ASX file. When Helix
Universal Server receives a request that contains the /asxgen/ mount point, it
sends a MIME stream that causes the browser to launch Windows Media
Player.
To stream to Windows Media Player 6.4, add the .asx extension to an ASXGen
link for an .asf, .wmv, or .wma clip. The extra .asx extension is not necessary if
you are streaming exclusively to Windows Media Player 7 and later, however. In
the following example, the URL is for video2.wmv.asx, even though the clip on
Helix Universal Server is video2.wmv. When it receives the request, Helix
Universal Server strips off the extra .asx extension:
<a href="http://helixserver.example.com/asxgen/video2.wmv.asx">Play Windows Media</a> |
Once Windows Media Player launches, Helix Universal Server streams the requested content using the MMS protocol. To circumvent restrictive firewalls, Helix Universal Server can also transmit an HTTP URL that duplicates the MMS link, enabling HTTP cloaking for Windows Media Players behind restrictive firewalls.
| For More Information: For information on enabling HTTP cloaking for Windows Media Player, see "Changing Port Assignments". |
Keep the following points in mind when linking Web page to streaming media clips.
Metafiles and the Ramgen and ASXGen utilities are mutually exclusive. If you
launch content with a Ram file, for example, make sure that the requested
URL does not contain the /ramgen/ parameter.
rtsp://helixserver.example.com |
rtsp://helixserver.example.com/video1.rm |
Conversely, when using Ramgen or ASXGen, make sure that your Web page link points to a streaming clip, not to a Ram file.
<a href="http://helixserver.example.com/ramgen/ |
<a href="http://helixserver.example.com/ramgen/ |
Remember that media clips and broadcasts stream over RTSP or MMS, but Web browsers can make requests only over HTTP. Specifying an incorrect protocol can prevent a presentation for launching, or degrade its playback. When using metafiles, ensure that URLs use streaming protocols.
|
|
When using Ramgen or ASXGen, make sure that your Web page link uses HTTP, rather than a streaming protocol such as RTSP or MMS.
<a href=" |
<a href=" |
Content creators may create SMIL presentations for RealOne Player. In this case, you treat the SMIL file as if it were a streaming media clip. That is, you link to the SMIL file from a Ram file:
rtsp://helixserver.example.com/presentation.smil |
or in a Web page link that uses Ramgen:
<a href="http://helixserver.example.com/ramgen/presentation.smil">...</a> |
The SMIL file itself then contains URLs to the various clips. These are typically RTSP URLs such as those you write in a Ram file:
<video src="rtsp://helixserver.example.com/video1.rm" region="video_region".../> |
| For More Information: RealNetworks Production Guide's clip source tags chapter explains SMIL URLs. |
You will need to give some information to content creators so that they can transfer their content to Helix Universal Server and write valid hyperlinks. The main reference manual for content creation, RealNetworks Production Guide, explains protocols, Ram files, and the Ramgen utility. However, content creators must rely on the Helix Universal Server administrator for the following information:
/ramgen/) to use to implement specific Helix Universal Server featuresHelix Universal Server is ready to stream clips as soon as it starts up. As the
quick start section "Creating and Streaming a Clip on Demand"
demonstrated, all you do is place a clip in the Content directory and write a
link as described in "Writing Links to Content". The following sections
provide information about additional, optional ways to configure Helix
Universal Server to stream clips on demand.
On your Helix Universal Server computer, you can create subdirectories under
the predefined Content directory, which is described in "Content Directory
Mount Point". On Windows, for example, you might create a video
subdirectory in the Content directory. In a default Helix Universal Server
installation on Windows, the full path would be the following:
C:\Program Files\Real\Helix Server\Content\video |
In an installation on UNIX, it may look like this:
/usr/local/Real/HelixServer/Content/video |
A Ram file link to a video clip in this subdirectory would include the video
subdirectory, but not the path to the main Content directory:
rtsp://helixserver.example.com/video/video1.rm |
If, for example, the link occurred in a Web page and used Ramgen, the video
subdirectory listing would follow the /ramgen/ mount point (and any other
mount points) in the URL
<a href="http://helixserver.example.com/ramgen/video/video1.rm">Play</a> |
If possible, place all of your streaming clips in the Content directory or its
subdirectories. If necessary, though, you can stream content from other
directories, disks, or networked machines. Instead of using symbolic links or
aliases from the Content directory to other directories, however, you create new
mount points for on-demand clips. Each mount point specifies a base path
where Helix Universal Server locates the files. You then use the new mount
point in URLs for on-demand clips located in the new directory.
| To create a new on-demand mount point: |
Tip:
You can also edit an existing mount point by selecting it
from the list, changing the information, and clicking Apply.
You can change the base path of the Content directory, for
example, by editing the RealSystem Content mount point
definition.
|
/video_clips/.No if you are using this server as a content-caching subscriber, and you do not want this subscriber to search content publishers for this mount point. For more on this feature, see "Content Caching".| Note: Even if you do not allow direct HTTP requests for the content, Helix Universal Server can deliver the content to media players over HTTP as necessary to work around firewall restrictions. Media players do not cache the content, though. |
This following table describes the ways in which on-demand streaming works with other features.
| Feature | Interaction with On-Demand Streaming |
|---|---|
| Simulated Live Broadcasting | You can use the Simulated Live tool (SLTA) to broadcast on-demand files as if they were live. See Chapter 10. |
| Live Archiving | If you have used the live archiving feature to convert live streams to on-demand files, you can then create links to these files and deliver them on demand. You can also use the archived files to recreate a live presentation using SLTA. |
| Helix Universal Proxy | Helix Universal Server is configured to allow Helix Universal Proxy to cache on-demand content streamed by Helix Universal Server. To prevent certain on-demand clips from being cached, see "Preventing Streams from Being Cached or Split". |
| Access Control, Authentication | Any access control or authentication rules you set up for Helix Universal Server are automatically used when users request on-demand content with RealOne Player. QuickTime Player support is limited to basic user name/password authentication. |
| Monitoring | You can view which presentations are streaming at any time with the Server Monitor. Click the Connections tab or the Files tab to see which files are in use. |
| Logging | All presentations streamed from Helix Universal Server, whether on-demand or live, are recorded in the access log. QuickTime and Windows Media Player connections are included. |
Aliases are substitutions for actual file names and directory paths used in URLs. With an alias, you can mask resources or simplify published URLs for any links that use any protocol. Suppose that the following example is a path to a file located on the physical disk of a Helix Universal Server:
C:\Program Files\Real\Helix Server\Content\music\pop\video1.rm |
In this sample, video1.rm resides a few subdirectories below the Content
directory. The following might be the unaliased URL for this file:
rtsp://helixserver.example.com/music/pop/video1.rm |
Using aliasing, you can assign the content music/pop/video1.rm to any value,
such as the following:
| Content: | music/pop/video1.rm |
| Alias: | example.rm |
Helix Universal Server would then play the video1.rm clip when a viewer
requested the following URL:
rtsp://helixserver.example.com/ |
Helix Universal Server replaces only the alias portion of the URL. If you enter characters in the URL before or after the alias, that part of the URL remains unchanged. For example, consider the following changes in the preceding resource-to-alias value pair:
| Content: | music/pop/ |
| Alias: | example |
For Helix Universal Server to play video1.rm, you would use the following URL:
rtsp://helixserver.example.com/ |
Here, Helix Universal Server replaces the alias with the exact characters in the resource, leaving the file name intact. If the preceding URL did not contain the file name, the resolved alias would lead to a subdirectory, not a clip.
You need to be careful to avoid content blind spotsor content that cannot be
accessed by a URLby using aliases that match resources. Suppose that you
had two files named video.rm and audio.rm in Helix Universal Server's Content
directory, and you created the following alias/resource pair:
| Content: | audio.rm |
| Alias: | video.rm |
The following URL would always play the audio.rm file:
rtsp://helixserver.example.com/ |
You would not be able to form a URL to play video.rm because Helix Universal
Server would always translate the characters video.rm into audio.rm. The only
way to write a URL to play the actual video.rm clip would be to create an alias
that uses the video.rm clip as its resource.
Observe the following considerations and limitations when setting up aliases:
/ramgen/ or /asxgen/ mount point. However, aliases do not function in HTTP URLs used by browsers to request Web pages.Creating an alias is a simple process that the following procedure describes.
| To map an alias to a resource |
The following table summarizes the Helix Universal Server features affected by aliasing.
Helix Administrator's content browsing feature allows you to list all on- demand clips residing on Helix Universal Server. You specify the mount points and types of clips, such as all clips or only the RealVideo clips, that you want to see. Helix Administrator then generates an HTML page listing and linking to all clips that fit those criteria.
| To create a content browsing list: |
/), which corresponds to the Helix Universal Server Content directory and its subdirectories.* in the Extensions to Browse box generates a content list for all clips and files, including SMIL files and metafiles such as Ram files. To limit the types of files shown, enter the file extensions in the box. Separate multiple extensions with a comma. For example, to browse just MP3 and RealMedia clips, you enter this:mp3, rm |
Just as browsers have "view source" commands that display HTML markup, RealOne Player has a view source command (View>Clip>Clip Source) that displays SMIL markup and clip information for all content it plays. When a viewer gives this command, Helix Universal Server generates an HTML page that contains the SMIL markup (if used), as well as information about clips and live broadcast streams. RealOne Player displays this information in a native browser window. With RealPlayer 7 and 8, source information displays in the viewer's default Web browser.
| Tip: The view source command is a handy way to learn a clip's streaming bit rate. Just play the clip in RealOne Player, and use the view source feature to display the clip's encoding statistics. SureStream RealAudio and RealVideo clips display all available bit rate streams. |
By default, source information is not divulged for any clip or presentation that requires user name and password validation. For other presentations, the source information hides clip locations. For example, when the viewer requests the source of a SMIL file, the browser's address box displays a URL that shows random numbers and letters in place of the SMIL file path:
http://helixserver.example.com:80/viewsource/template.html?ABcdlkj293847 |
The source page displaying SMIL markup links to separate pages that give information about each clip used in the presentation, including clip size, buffer time, and bit rate, but not the full path. To protect the location of content, the SMIL source page omits the full path to the clips, showing ellipses (...) instead. For example, the actual SMIL file on Helix Universal Server may have a source tag that gives the full URL to a video clip:
<video src="rtsp://helixserver.example.com/presentation/presentation.rm" .../> |
In the SMIL source page that viewers see, the full path is hidden:
<video src="rtsp://.../presentation.rm" .../> |
When you stream with Helix Universal Server, you have full control over what information you display for which clips. You can override defaults, for example, and display path information for all clips, or only for those in selected directories. Other methods of playing clips do not offer this full control, however:
By default, the view source feature is turned on for all on-demand clips and broadcasts, except those that require user name and password validation. The full paths to clips and files are not displayed, however. On a system-wide basis, you can turn off the view source feature, or decide to show full path information for all clips that do not require password validation. Or, you can set up selective rules to define exactly which on-demand clips and broadcasts display source information.
To enable selective rules, you define paths to content directories and broadcast
mount points. The main on-demand mount point (/) is predefined to let you
set up a source rule for the entire Content directory. You can add more rules for
Content subdirectories, other on-demand mount points and subdirectories,
and broadcast mount points such as /broadcast/. In applying view source rules,
Helix Universal Server looks for the closest match. The examples in the
following table illustrate how these rules work.
| For More Information: See Chapter 7 for information about broadcast mount points. |
The following procedure explains how to change the view source settings. You need to change these settings only if you want to modify the defaults to turn off view source entirely, for example, or to set up selective viewing rules.
| To change view source settings: |
If you want to enable selective viewing rules, select Use Settings Above as the master view source setting. You can use the master setting Hide All Paths or Show All Paths with selective rules. If you want to hide paths on a case-by-case basis, though, select Use Settings Above.
/), which corresponds to the Content directory in the main Helix Universal Server installation directory. Do the following to define a new path:Content/news/ subdirectory you've created, for example, you enter /news/. (The mount point "/" corresponds to the Content directory.)No, the Hide Paths setting does not matter.The following table describes how the view source feature interacts with other Helix Universal Server features.
| Feature | View Source Interaction |
|---|---|
| Broadcasting | The view source feature applies to both on-demand and live content. |
| SLTA | On-demand files that are converted to live streams through SLTA show the same information as other live files. |
| Splitting | View source is disabled for users who are receiving a broadcast through a push splitting source. |
| Authentication | The view source feature is automatically disabled for all secure content. |
| Reporting | A record is created in the access log when a user makes a view source request. See the table "GET Statements for On-Demand Content". |
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