Plugin error with Intermedia

Question

Background:
table with 8 text fields, 3 Intermedia fields (1 audio, 1 video, and 1 image) where binary data is stored in the table
I have a JSP page that pulls the text data from the database.
I have a servlet that pulls the audio and video data from the database.
The JSP references the servlet via a link - If I right click on the link, and select "save as...", I can save the audio and video data to disk, and it runs fine. The problem is if I want to just click on the link and spawn the audio/video plugin (in my case Windows Media Player). I get the following error - "Cannot determine the device type from the given filename extension".
Within the servlet, I set the responses content type to the mime type of the Intermedia object. I then open an output stream from the Intermedia object, and write the data out to the stream.
Are there any other HTTP headers that I need to set to get the plugin to work properly? How can I get the data to show a filename instead of the long URL query string?
Thanks.
Troy

Answer 1

Hi,
I suspect the problem here is that the plugin is looking for a file extension to decide the type of media that is to be played. I've seen this problem with some plugins with the Netscape browser, but not (so far) with Microsoft's IE browser.
Here's what I think happens in Netscape: the browser gets the response and decides which plugin to use based on the Content-Type (MIME type) header. It saves the content in a file in its cache, then passes the filename to the plugin. However, as the URL doesn't have a file name/extension, then the file name in the cache doesn't have an extension either. This means that a plugin that can handle multiple content types, but that doesn't parse the content to determine the type, doesn't know what to do. For example, the Windows Media Player doesn't parse the content, so it has to rely on the file extension to know how to play the content. However, the Quicktime plugin works fine with most media it handles because it parses the content to determine how to play it. In this situation, I've seen problems with .WAV and .AVI files.
I'm less sure exactly how IE handles things, but I do know that it relies heavily on a combination of file extensions and parsing content to determine the MIME type heuristically. That is to say, IE knows about a whole bunch of 'signatures' at the beginning of content from which it can determine the content type. So even if it doesn't have a file extension, it can figure things out. I believe it also does some form of sanity checking between the file extension, if there is one, the content-type header, if there is one, and the content type that it determines itself using its own heuristic algorithms, but I don't remember the details. Of course, this approach can also cause problems. For example, even slightly older versions of IE don't recognize the format of some of the newer versions of, for example, Microsoft Word. (I ran into this one myself not so long ago.)
In your case, I think there are a couple of options:
[list=1]
[*] Include a dummy file extension when you build the URL to fetch the audio or video data, or
[*] Use a plugin that can determine the MIME type dynamically.
[list]
Option 1 is fairly simple and has the advantage that it'll always work, no matter what browser and/or set of plugins is being used. I suspect there are a bunch of ways to do this, but here are a couple of ideas:
[list=1]
[*] When building the URL, include a dummy query string parameter (use any name you like) that contains the extension. I don't understand exactly how this gets parsed (it may be that the plugin simply searches the entire URL for known/supported extensions), but the following should work:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>multimediaservlet?pkey=pkeyvalue&paramname=extension<HR></BLOCKQUOTE>
Eg:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>multimediaservlet?pkey=forty2&foo=.avi<HR></BLOCKQUOTE>
Of course, you might want to use something more reasonable :-)
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>multimediaservlet?pkey=forty2&ext=.avi<HR></BLOCKQUOTE>
[*]I've not tried this myself, but you should be able to build a dummy file name and include it in the UTL after the servlet name. The servlet can then get the file name (by calling HttpServletRequest.getPathInfo), decode what it needs (ie, extract the key), then retrieve and deliver the data:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>multimediaservlet/pkeyvalue.extension<HR></BLOCKQUOTE>
Eg:
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>multimediaservlet/forty2.avi<HR></BLOCKQUOTE>
This method has the advantage that it will provide a default file name for a Save-As operation.
[list]
Hope this helps,
Simon
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