Delivering enclosures to IE7 and Windows

The feed syndication platform built-in to Internet Explorer 7 and Windows Vista may fail to download media enclosures larger than 15 MB. It’s a feature, not a bug, designed to prevent over consumption of computer bandwidth.

The automatic download engine built-in to Windows (BITS) tries to queue up audio, video, or other enclosure content in a user’s subscription updates. It tries to be polite and not consume all available bandwidth, throttling back its consumption while higher priority tasks such as e-mail and web browsing receive new data.

The download engine prefers to download large files in pieces, requesting an achievable bite-sized chunk of your content instead of trying to swallow the whole file at once. It’s also easier to start and resume a download when you request one small piece at a time.

The download engine sends a request to your server and hopes it supports sending files in chunks, more technically known as an HTTP Range. A server can advertise its support for chunked downloads by sending an Accept-Ranges response header value of bytes. If your server does not support chunked downloads and the requested file is less than 15 MB the download engine will attempt another request using HTTP GET.

Most modern web servers support range requests, but if you routinely deliver files larger than 15 MB you should double-check and possibly upgrade your server software to help insure your published data arrives at its intended destination.

  • Posted
  • Updated at
  • Comments [2]


Commentary on "Delivering enclosures to IE7 and Windows":

  1. Geald Buckley on wrote:

    As the majority of our podcasts are well under this 15 MB range I feel pretty good about being delivered. However, a few will necessitate a larger file size. We’re no different than anyone else: most of the platform and agents in our log files are some combo of Win and IE.

    Thanks for tipping us off to this. It wouldn’t have been fun to deal with this kind of bugaboo in such large quantities. At least now I can go check to see if the servers advertise the chunked DLs.

    Much appreciated!

  2. Padova on wrote:

    It’s easy to overcome the 15 MB limit – just set the registry value HKCUSoftwareMicrosoftFeedsMaxEnclosureSize (DWORD) to a suitable value (in kB). If you are writing a podcast app that uses the common feed list, this is easy enough to adjust.