I tried to play a .mp4 video from a website ( with the HTML5 Video Tag ) with the UIWebView. 
The iPhone / iPad Device and Simulator only shows a black frame with a struck out play button. 
If I just called this website on the Safari Mac Version, it is possible to play it.
Whats the matter?

It isn't a local file. The html looks like this:

```
    <?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta charset="utf-8" />
        <link rel="stylesheet" type="text/css" href="../css/shared-culture.css" />
    </head>
    <body>
        <section class="base">
            <hgroup>
                <h1>creative commons</h1>
                <h2>a shared culture</h2>
            </hgroup>

                <p>To celebrate our 2008 fundraising campaign, Creative Commons has
                    released “A Shared Culture,” a short video by renowned filmmaker <a
                        href="http://en.wikipedia.org/wiki/Jesse_Dylan">Jesse Dylan</a>. Known for
                    helming a variety of films, music videos, and the Emmy Award-winning <a
                        href="http://my.barackobama.com/page/invite/yeswecanvideo">“Yes We Can”</a>
                    Barack Obama campaign video collaboration with rapper will.i.am, Dylan created
                    “A Shared Culture” to help spread the word about the Creative Commons mission. </p>
                <!-- height="240" width="360" -->
                <video id="video1" controls="controls">
                    <source src="../video/shared-culture.mp4" type="video/mp4"/>
                    <source src="../video/shared-culture.webm" type="video/webm"/>
                    <div class="errmsg">
                        <p>Your Reading System does not support (this) video.</p>
                        <pre><code>
&lt;video id="video1" controls="controls"&gt;                    
  &lt;source src="../video/shared-culture.mp4" type="video/mp4"/&gt;
  &lt;source src="../video/shared-culture.webm" type="video/webm"/&gt;    
&lt;/video&gt;
                        </code></pre>
                    </div>
                </video>
                <p>In the video, some of the leading thinkers behind Creative Commons
                    describe how the organization is helping “save the world from failed sharing”
                    through free tools that enable creators to easily make their work available to
                    the public for legal sharing and remix. Dylan puts the Creative Commons system
                    into action by punctuating the interview footage with dozens of photos that have
                    been offered to the public for use under CC licenses. Similarly, he used two
                    CC-licensed instrumental pieces by Nine Inch Nails as the video’s soundtrack
                    music. These tracks, “17 Ghosts II” and “21 Ghosts III,” come from the Nine Inch
                    Nails album Ghosts I-IV, which was released earlier this year under a Creative
                    Commons BY-NC-SA license. (See <a
                        href="http://creativecommons.org/videos/a-shared-culture">attribution</a>.)
                </p>

        </section>

    </body>
</html>

```