[streaming] Streaming WAV / Converting WAV to a streamable format on the fly

[Guido Helmers]

Hi,

I am trying to implement a web application that allows the user to playback 
WAV files inside a web browser.


__________
Background
__________
- The file server stores audio files as GSM 6.10 or TrueSpeech encoded WAV 
files.
- The web server (most probably ASP.NET on IIS) offers the client the 
ability to search audio files on the file server (a different machine).
- The client will be equiped with internet explorer and a standard Media 
Player plugin (preferably Windows Media Player or QuickTime).


____________
Requirements
____________
The requirements for this application are:
1. The client should be able to playback a WAV file with a media player 
plugin in the web browser.
2. The WAV file should NOT be accessible to the client, the URL to the WAV 
file should not be accessible / visible
3. The WAV file should NOT be downloaded
4. The WAV file should NOT be cached on the client hard disk


________________________
No Progressive download!
________________________
Because of requirement 2, we can NOT do this:
<object id="player" height="45" width="220" 
classid="CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6">
  <param name="url" value="audio/GSM.wav" />
</object>
because the user can copy-paste the file location from the source code, and 
easilly download the file.

Because of requirement 3 and 4, pseudo streaming like the following (an 
asp.net example) is NOT allowed, because the complete file is still 
downloaded to the client:
<object id="RPPlayer" height="200" width="220" 
classid="CLSID:CFCDAA03-8BE4-11CF-B84B-0020AFBBCCFA">
  <param name="type" value="audio/wav" />
  <param name="src" value="audioStream.aspx" />
</object>

code-behind page of audioStream.aspx:
...
Response.ContentType = "audio/wav"
Response.AddHeader("Content-Disposition", "attachment; 
filename=""GSM.wav""")
Response.TransmitFile("C:\GSM.wav")
...


_______________
Real Streaming?
_______________
So having excluded downloading and pseudo-streaming (a.k.a. http-streaming 
a.k.a. progressive download) the logical next step is 'real' (on demand) 
streaming.
The limitation that we come across when using standard Streaming Servers 
(like Windows Media Services or QuickTime) is that they can not stream WAV 
files.

The WAV files always have to be encoded to a streamable format (WMA for 
windows media service, or MOV for QuickTime/Darwin, etc) before they can be 
streamed.

Converting the complete file server from WAV to a streaming format (WMA, MOV 
or whatever) is not an option (because the file server is being populated 
with new WAV files continuously; this process is 'hardware-driven' and 
extremely hard to adjust). We will stick to the WAV file format for now.


_________
Questions
_________
So what I'm really looking for is one of the following:

(a) a streaming server that can stream WAV files.
Does this exist or is it technically impossible to stream WAV files? Why?

(b) or a way to convert WAV to a streamable format on the fly 
(programmatically, 'inside' the streaming server), when the user requests 
the WAV file.
I have no problem with converting WAV on the fly,
- but the conversion should never take more than a few seconds for a one MB 
WAV file (= 10 minutes in our case),
- and I would like to hear experiences from other developers that have done 
this, before I invest a lot of time in this and bump into unforeseen 
problems when I'm halfway.

I noticed that a 10 minute WAV file which is 1MB in size takes about
- 3 seconds to convert to MOV with QuickTime Pro (I think this can be 
programmed into the Darwin streaming server)
- 25 seconds to convert to WMA with the Windows Media Encoder (could be 
programmed with the Windows Media SDK but 25 seconds takes way too much 
time)
- Is there a way to programmatically convert to a format that can be 
streamed by vlc, on the fly?

(c) or a completely different approach, like streaming over HTTP with to 
Java applet.
I can not find any examples on the web, and think this might be the most 
time-consuming solution of all?

Other helpful comments are also very welcome...

Cheers,

Guido

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