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Table of Contents

  1. Introduction
  2. Flash media communication protocol: RTMP
  3. Supported file types
  4. Streaming vs. HTTP delivery
  5. Video delivery techniques in Flash

Overview of streaming with Flash Media Server 3

Streaming vs. HTTP delivery

When determining a method of delivery for video over the Internet in the Adobe Flash Player, you have three choices:

  • Embedded video
  • Progressive download
  • Streaming

Embedded video is rarely used except in very specialized applications with low-quality, short video clips, so I'll just discuss streaming vs. progressive here.

In both progressive and streaming delivery, the video content is kept external to the SWF file. To deploy to the web, the SWF file and the video file would both be uploaded to a server.

Keeping the video external and separate offers a number of benefits over the embedded video method, including:

  • Easy to update and accommodate dynamic content: It's relatively easy to add or change content independent of the video player and without the need to republish the SWF file.
  • Small SWF file size: Your SWF file can remain very small for fast page loads; then the video can be delivered when the user requests it.
  • Better performance: Because the FLV and SWF files are separate, the viewer will have a better playback experience.

Note: Although the focus in this section is on the delivery of video files, the same methods can be used to deliver audio files. In other words, audio files can also be embedded, progressively downloaded, or streamed.

Progressive download video delivery

Since Flash MX 2004, progressive download has been supported for video delivery. This method allows developers to load external video files into a Flash or Flex interface and play them back during runtime. This can be accomplished using ActionScript commands with the Video object or playback components, or by setting parameters for the playback components in the authoring environment (see Figure 2).

Figure 2

Figure 2. Parameters set for an FLVPlayback component to STREAM an external video file into a SWF

When the video is played, the video file first begins to download to the viewer's hard drive, then playback starts. The video will begin to play when enough of it has downloaded to the viewer's hard drive. The file is served from a standard web server through an HTTP request, just like a normal web page or any other downloadable document.

In comparison to streaming video, there's really only one consistent benefit to progressive download—you don't need a streaming server to deliver the video. Progressive download video can be served from any normal web server.

While this can be convenient and potentially cost-effective, the following potential issues should be noted:

  • There are limited seek and navigation capabilities
  • Viewers can access and repurpose content

Progressive download is a perfect use for hobbyists or websites that have low traffic requirements, don't mind if their content is cached on the viewer's computer, and only need to deliver shorter length videos (under 10 minutes). Customers who need advanced features and control over their video delivery, and/or those who need to display video to larger audiences (e.g. several hundred simultaneous viewers), need to track and report usage or viewing statistics for the video, or want to offer the best interactive playback experience, will need to stream their video. Streaming delivery also consumes less bandwidth than progressive delivery, because only the portion of the video that is watched is actually delivered.

Streaming video delivery

When you use streaming delivery, as is the case with progressive download, the video files are kept external to the other content. Developers can use ActionScript commands (and parameter settings with media components) to load external video files into a SWF and play them back at runtime. In fact, the ActionScript code needed for streaming is almost identical to that for progressive download.

This is where the similarities between progressive download and streaming delivery end. In the case of streaming video, each client opens a persistent connection to the streaming server, and the server streams the video bits to the client. Those bits are displayed by the viewer and then immediately discarded.

This tight connection between the server and the client, and the server's ability to precisely control and deliver any portion of a stream as requested, enables the developer to take advantage of some advanced capabilities. These include the following:

  • Determining the client bandwidth and serving a stream with an appropriate bitrate.
  • Measuring and tracking the stream's quality of delivery and switching to a lower (or higher) bitrate stream if needed—if network congestion increases, for example.
  • Automatically generating thumbnails or play short previews of your video clip without having to create separate image or video clips, and without downloading the entire video in the background.
  • Automatically creating "chapters" (with appropriate thumbnails) that can be used for navigation of longer videos, without having to break the video up into smaller files.
  • The ability to seamlessly switch mid-stream from one camera angle, or one stream to another.
  • The ability to "edit" video clips together to create one continuous video for playback. For example, playing the first 10 seconds of clip 1, followed by the content between the 30- and 40-second marks of clip 2, followed by the last 20 seconds of clip 3.
  • The ability to webcast live or recorded events where all viewers see the same thing at the same time.

If progressive download is a "dumb" method of video delivery with very little control—it's basically a simple HTTP download call—then streaming is a very "smart" method of media delivery that enables publishers to control every aspect of the video experience.

Why streaming is better

The advantages of streaming video from Flash Media Server are numerous:

  • Fast start: Streaming video is the fastest way to start playing any video on the web.
  • Advanced video control: Features such as bandwidth detection, quality-of-service monitoring, automatic thumbnail creation, server-side playlists, and more.
  • Efficient use of network resources: Customers who pay for their video hosting or bandwidth by the amount that is transferred will benefit from streaming video, since only the bits that the client actually views are transferred.
  • Secure, protected media delivery: Because the media data is not saved to the client's cache when streamed, viewers can't retrieve the video or audio file from their temporary Internet files folder. There are also additional security features in FMS 3 that prevent stream ripping and other risks to your file's security. Refer to the article, Scaling and securing streaming media applications with Flash Media Server 3, for more details.
  • Minimal use of client resources: Resources such as memory and disk space are significantly reduced with streaming, because the clients do not need to download and store the entire file.
  • Tracking, reporting, and logging capabilities: Because progressive download is just a download of a file, you can't easily log specific relevant statistics such as how long the video was viewed; if the user navigated forward, backward, or paused the video; how many times the viewer played the video; if the viewer left the web page before the video completed playing, etc. Streaming enables you to easily capture this important data.
  • Full seek and navigation: Viewers can immediately seek to any point in the video and have it start playing immediately from that point. This makes streaming a great solution for longer-playing videos or applications such as video blogging, classroom lectures, and conference sessions, where you may want to jump into the video at a specific point rather than requiring the viewer to watch it from the beginning.
  • Deep interactivity: The precise control found in streaming enables developers to create extensive interaction in their video applications. For example, the ability to switch camera angles, have one video spawn another video, or seamlessly switch to alternate endings are all enabled by streaming.
  • Live video: Streaming provides the ability to deliver live video and audio from any connected webcam or DV camera, and even directly from some video cards, natively in Flash Player.
  • Video capture and record (FMIS only): In addition to live streaming, Flash Media Server also gives you the ability to record video either in conjunction with the live stream (e.g. for archiving an event) or on its own (e.g. video messaging).
  • Multiuser capabilities (FMIS only): In addition to live one-to-many streaming, Flash Media Server also enables multiuser streaming of audio, video, and data for the creation of video communication applications.

While streaming may be perceived as being more difficult than progressive download, they're actually extremely similar—they both use the same components and the same ActionScript commands. Streaming just gives the developer more power to create rich, interactive video applications.

The only potential downside to streaming is that it requires special server software. Just as a robust data application would require you to install an application server in addition to your web server, robust media delivery applications require a streaming server in addition to the web server.

Customers with high-volume streaming needs, popular content, or critical uptime requirements who don't want to build their own infrastructure can get the benefits of streaming video in Flash Player by utilizing a Flash Video Streaming Service (FVSS). These Adobe partners offer load-balanced, redundant deployment of FMS over a reliable content delivery network.

When to choose streaming

Streaming with Flash Media Server should be used in any situation where you want or need to do the following:

  • Deliver long files (10 minutes or longer) or high-bitrate files (high-definition)
  • Perform bandwidth detection, delivering the best quality for available hardware
  • Use quality-of-service monitoring
  • Support real-time tracking
  • Provide real-time data sharing and interactivity to your video experiences
  • Stream live video and/or audio
  • Record video and/or audio
  • Serve more streams with less bandwidth

If your website or blog relies heavily on video, audio, or real-time data sharing for delivering your message, you will want to present it in the best possible manner by utilizing the features of Flash Media Server.

Where to go from here

Be sure to read the following articles to learn more about streaming video:

For a summary of the topics presented in this article, the table on the next page compares the three video delivery techniques in Flash.

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