Re: How to valid a WMV file pragmatically

From: Chris P. (msdn_at_chrisnet.net)
Date: 11/05/04 

Date: Fri, 5 Nov 2004 08:39:26 -0500

On Thu, 4 Nov 2004 09:49:26 -0500, Chris P. wrote:

> On Wed, 3 Nov 2004 17:43:50 -0500, Chris P. [MVP] wrote:
>
>> Scott Dever wrote:
>>> Can anybody point me to which interface/code to use to valid a WMV
>>> file pragmatically?
>>
>> The easiest way is with DirectShow. If you're not dealing with DRM see the
>> PlayWnd sample in the SDK which plays most all media types including WMV
>> (once you remove the cripple feature). If you're dealing exclusively with
>> WMV/ASF then see the PlayWndASF sample.
>
> Nevermind me. I read your question wrong.

Because WMV files are streams, the old way to 100% validate the file is to
read the entire file. Obviously there are alternatives, if the file is
indexed. You can seek to several key points in the file and make sure you
can read without error which gives a reasonable confidence. The most
common corruption in internet trasmission is truncation.

Also playing a file in DShow without a graph clock or with the Format SDK
will occur at a reasonable speed but use a lot of CPU. Alternatively you
could write a DShow filter that was able to validate a ASF stream and
connect it in place of the decoder. You would be able to run the graph at
a very high rate because no decoding or rendering would be occuring. The
spec for the file format and stream is here:
http://www.microsoft.com/windows/windowsmedia/format/asfspec.aspx

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