PRB: Intelligent Streaming May Cause Windows Media Player to Drop Video Stream (294184)


The information in this article applies to:

  • Microsoft Windows Media Player 6.4
  • Microsoft Windows Media Player 7
  • Microsoft Windows Media Player 7.1
This article was previously published under Q294184

SYMPTOMS

Windows Media Player (WMP) uses the intelligent streaming feature to detect unfavorable network conditions and adjust the properties of a video stream to maximize quality. Using intelligent streaming, WMP may request that the server reduce the bandwidth requirements of the video stream or completely stop streaming video. However, in certain scenarios, it may not be desirable to reduce the quality of the video stream in place of rebuffering.

RESOLUTION

WMP 7.1 includes a new feature that disables Intelligent Streaming. When you disable Intelligent Streaming in WMP 7.1, the player will rebuffer by default.

To work around this problem, use the "WMThinning=0" URL-modifier in scenarios where any of the following is true:
  1. The network bitrate is too low to stream the audio/video stream combination that the player selects.
  2. The network connection suffers from sudden drops in the bitrate.
During the above conditions, it is preferred that the player periodically rebuffer instead of trying to switch to a lower bitrate stream or to "thin" the video stream (in which only key-frames are displayed.)

NOTE You should only use the "WMThinning=0" modifier with URL schemes that use Transmission Control Protocol (TCP) for data delivery. For WMP 7 and WMP 8, this means mmst:// and http:// URLs.

You can also use "WMBitrate=nnn" together with "WMThinning" on the same URL, where "nnn" is the network bitrate in bits per second. If WMP is configured to automatically detect the link bitrate, the player uses the bitrate that you specify in the "WMBitrate" URL modifier as the link bitrate. WMP's notion of the link bitrate affects which audio/video stream combination the player initially chooses.

You can use the "WMBitrate" modifier in scenarios where you suspect that WMP is not correctly detecting the link bitrate and, as a result, chooses a suboptimal audio/video stream combination or unnecessarily chooses to thin the video stream.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

MORE INFORMATION

The "WMThinning=0" modifier turns off bandwidth switching, which in turn may cause thinning. Although intelligent streaming is the official term for some of the player's advanced networking capabilities, bandwidth switching is essentially the same as intelligent streaming.

When network conditions are poor, WMP asks the server to switch to a lower bandwidth video stream (which is where the term "bandwidth switching" comes from). If the server is already streaming a video stream at the lowest possible bandwidth, WMP asks the server to thin that stream instead, in which the server only sends video key-frames. Finally, if network conditions still do not improve, WMP asks the server to turn off the video stream completely.

As the previous paragraph describes, thinning is one part of bandwidth switching. However, you can also refer to everything in the previous paragraph as thinning because initially WMP asks the server to "thin" the bitrate by switching to a lower bitrate stream. Then, WMP asks the server to "thin" the bitrate by only sending video key-frames. Finally, WMP asks the server to "thin" the bitrate by dropping all video frames.

WMP normally enters a buffering state at the beginning of the stream. This is normal and is an attempt to maximize quality when the playback begins. However, if intelligent streaming/bandwidth switching/thinning fails to do what it is supposed to do, buffering can occur in the middle of playback.

Thus, WMP can use buffering any time after the beginning of playback as a last resort when the normal intelligent streaming mechanism does not work, or when intelligent streaming is explicitly disabled through the "WMThinning" URL-modifier.
Modification Type:MajorLast Reviewed:11/14/2003
Keywords:kbprb KB294184
©2003 Microsoft Corporation. All rights reserved.