Flash Streaming vs Progressive Download

February 3, 2010

This is a brief description of Streaming vs Progressive Download with Flash and how it relates to web video.

Progressive Download

This is a common way people link to videos from their own websites. They encode a video, upload it to their website then embed the video.
When someone views this video it is downloaded to their computer. The web server does not care about the quality or size of the video, it will allow them to download it like any other image or document as fast as they can. Playback will begin as soon as enough video has been downloaded, but you are not able to fast-forward to the end of the video without it being downloaded.
To get a little more technical this transfer happens over HTTP (Hypertext Transport Protocol) which operates on TCP (Transport Control Protocol). These protocols make every little bit of video that is downloaded to your computer will be a little larger than it needs to be. This is to ensure that every piece of data is guaranteed to be delivered and if it isn't the data is sent again, using a little more bandwidth. If someones internet is interment you can end up using more bandwidth for resending information than for the video itself.
TCP (progressive download) is not designed for efficient real time delivery or careful bandwidth control. But if you need a file accurate and reliable then it will deliver every time.
When the h.264 codec was released this introduced another flaw in progressive downloads. h.264 has the information to play the video at the end of the file, so the whole file must be downloaded before the video can start to play. (This was fixed with Flash player 10)
Key Points:

  • cannot be used for live events
  • is not efficient
  • is not secure
  • can not adjust for a users connection speed
  • can not jump to video without it being downloaded
  • video is downloaded

Streaming (Flash Media Server)

Streaming is more efficient and less common because you need FMS software running on a web server to use it. It works similar to embedding a video on a website using progressive download. The videos is encoded, uploaded to a FMS then embedded on a website.
When someone views the video a well made player will detect the viewers connection speed and buffer a little video, not downloading the whole file. A viewer will be able to fast-forward to any place in the file without having to download it.
To get more technical the videos are transferred over RTMP (Real Time Messaging Protocol) or RTMPS which has little overhead compared to HTTP. Every little piece of video that is sent to your computer will be just enough to view the video. If someones connection is interment then the video will pause, re-buffer and start when the connection is better. This is a more efficient use of bandwidth.
Also if RTMP (port 1935) fails it will fall back to RTMPT which will send the packets over HTTP, but will not need to resend information as with progressive download.
Using FMS and streaming videos you can also apply security by IP viewing the video or web page the video is streaming from.
Key Points:

  • can be used for live events
  • used for advanced interactive content
  • is efficient
  • adjusts for connection speeds
  • video is not downloaded
  • better analytics (how many seconds viewed)

Posted by Beau Durrant

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