Archived:Streaming 3GP multimedia content to Flash Lite using RTSP
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20 Jun
2010
Contents |
Streaming 3GP multimedia content to Flash Lite using RTSP
This article explains how to set up 3GP streaming using Real-Time Streaming Protocol (RTSP) in Flash Lite from Adobe.
Prerequisite
Flash Lite 3.x
All details mentioned in this article have been tested on Flash Lite 3.0 devices on Symbian S60 3rd Edition mobile devices.
Darwin Streaming Server
Darwin Streaming Server (DSS) is an open source, free-to-use streaming server from Apple. The commercial version of this server is the Quick Time Streaming Server. The open source version can be downloaded from the following link:
http://static.macosforge.org/dss/downloads/DarwinStreamingSrvr5.5.5-Windows.exe
Perl
Perl is a prerequisite for DSS installation. Install it before installing DSS:
http://www.activestate.com/activeperl/downloads
MP4Box
MP4Box is a tool used for “hinting” the 3GP media files. It can be downloaded from the following location:
http://www.videohelp.com/tools/mp4box
QuickTime Player (optional)
Introduction
There are two major methods of multimedia content delivery on the internet:
1. Streaming
2. Progressive download
Streaming makes use of RTSP/RTP/RTCP protocol stacks to deliver real-time media content over the Internet. It runs on top of the UDP protocol stack, hence the delivery of RTP packets is not guaranteed. The player has to employ error concealment algorithms to compensate for the lost packets. However, this method is fast and there is no retransmission overhead, making it the right choice for real-time media delivery applications such as Live TV, video conferencing, and so on. An RTSP streaming server such as Darwin or Helix is required.
Progressive download, on other hand, uses the same set of protocol stacks that are used for downloading a web page by a browser—namely, HTTP over TCP/IP protocol stacks. However, the player doesn’t wait for the entire media file to be downloaded and can start the playback as soon as sufficient data required for the codec to start decoding has been received. This provides the benefit of having guaranteed delivery, hence the player doesn’t have to worry about error concealment. As a result, the video plays without any artifacts. This method requires a standard HTTP server such as Apache.
Another option for streaming is using RTMP, which is a proprietary protocol of Adobe developed for streaming audio/video data to Flash. RTMP also employs a TCP/IP protocol stack. It tries to achieve real-time delivery over a reliable connection. Most Content Delivery Networks (CDNs) deploy RTMP for flash streaming. The method requires Adobe Flash Media Server or Wowza. Red5 is an open-source flash-streaming server.
A detailed discussion of streaming and progressive download is beyond the scope of this article.
Flash Lite 3.x supports both HTTP-based progressive download and streaming. The codecs below can be used with each of the delivery mechanisms:
|
|
Media Container Format |
Video Codec |
Audio Codec |
|
Progressive Download |
FLV |
On2 VP6/Sorenson Spark |
MP3 |
|
Streaming |
3GP/MP4 |
MPEG-4/H.264/H.263 |
MP3/AAC |
For a more detailed list of supported codecs, please see the device specifications at:
http://www.developer.nokia.com/Devices/
Because this article addresses streaming, the discussion will be restricted to 3GP files. 3GP is a container for audio and video data. Video can be encoded using MPEG-4/H.264/H.263 codecs; audio can be encoded using the MP3 or AAC codec. Other formats may be possible but were not tested. The following is the recommended video specification for 3G:
Resolution – 320 x 240
Frame rate – 25 frames per second (fps)
Bit rate – 360 KBps (Kilo Bits Per Second)
The recommended audio encoding is:
Sampling rate – 44.1 KHz
Channel – Stereo
Bit rate – 128 KBps
The above settings offer a good trade-off between the available 3G channel bit rate and quality. H.264 outperforms MPEG-4 and H.263, that is, it gives much better visual quality for the same bit rate. Similarly, AAC outperforms MP3 for audio. The encoding parameters, such as codec, bit rate, frame per second, audio sampling rate, and so on, can be decided based on the application needs, available bandwidth, and device capabilities.
Typically for 3G, a bit rate of 260 to 500 KBps gives a good performance and offers a good trade-off between bit rate and quality. Once the 3GP file is created, it has to be “hinted” by MP4Box to allow DSS to stream that file. Use the following command for hinting:
Mp4box –hint filename.3gp
If hinting is not done, the player will give an unsupported format error. Once “hinted”, the files can be placed in the following folder and streamed using DSS:
C:\Program Files\Darwin Streaming Server\Movies
Darwin installation
The path given for the Movies (above) is the default location of the Darwin installation. The steps for installing DSS are as follows:
Extract the DSS setup to any desired location.
Browse to that location and double click on install.bat. The installation will begin.
You will be asked for an admin password, which can be specified, or simply press Enter for no password.
DSS is installed as a service and there is no need to launch it manually.
DSS can be viewed in the list of running services (start->control Panel->administrative Tools->Services).
To test the installation, enter the following URL in the QuickTime Player. Audio and video must play.
Rtsp://IP-ADDRESS/sample_50kbit.3gp
Flash Lite coding
Coding for video playback using Flash Lite is pretty straightforward. In Adobe Flash CS4, place a video object on the stage by right-clicking on the library, selecting New Video, and then dragging the symbol to the stage. Give an instance name ‘videowindow_vid’ to the component. Put the following code in the script:
videowindow_vid.play("rtsp://10.55.104.74/sample_50kbit.3gp");
videowindow_vid.onStatus = function(status_obj:Object) {
//handle status “"completed"”
};
The onStatus handler is invoked only for ‘completed’ status. To play back local 3GP files, instead of the URL, use only the file name with the appropriate path.
Limitations
The following are the limitations of 3GP in Flash Lite:
1. Because the native player is used, nothing can be overlaid on top of the video.
2. A streaming server is required.
3. The content requires modifications—the 3GP clips need hinting for DSS. If only audio streaming is desired, the audio (AAC) needs to be packaged as 3GP and hinted for it to work on a Nokia device.
4. No metadata information or player status information is received. Thus, a mechanism for separately delivering the metadata information for the media files has to be provided so that the player can show the duration, progress, and so on. Also, if the player buffers, the status cannot be shown to the user.
5. Flash Lite volume control doesn’t work, so the application has to rely on the hardware volume keys for control.
