Pass the decryptedUrl to the MFileBody so that it doesn't need to decrypt it itself.

src/components/views/messages/MAudioBody.js

@@ -81,7 +81,7 @@ export default class MAudioBody extends React.Component {
         return (
             <span className="mx_MAudioBody">
                 <audio src={contentUrl} controls />
-                <MFileBody {...this.props} />
+                <MFileBody {...this.props} decryptedUrl={this.state.decryptedUrl} />
             </span>
         );
     }

src/components/views/messages/MFileBody.js

@@ -28,7 +28,7 @@ module.exports = React.createClass({
 
     getInitialState: function() {
         return {
-            decryptedUrl: null,
+            decryptedUrl: (this.props.decryptedUrl ? this.props.decryptedUrl : null),
         };
     },
 

src/components/views/messages/MImageBody.js

@@ -19,7 +19,8 @@ limitations under the License.
 var React = require('react');
 var filesize = require('filesize');
 
-var MFileBody = require('./MFileBody');
+import MFileBody from './MFileBody';
+
 var MatrixClientPeg = require('../../../MatrixClientPeg');
 var ImageUtils = require('../../../ImageUtils');
 var Modal = require('../../../Modal');
@@ -184,7 +185,7 @@ module.exports = React.createClass({
                             onMouseEnter={this.onImageEnter}
                             onMouseLeave={this.onImageLeave} />
                     </a>
-                    <MFileBody {...this.props} />
+                    <MFileBody {...this.props} decryptedUrl={this.state.decryptedUrl} />
                 </span>
             );
         } else if (content.body) {

src/components/views/messages/MVideoBody.js

@@ -147,7 +147,7 @@ module.exports = React.createClass({
                     controls preload={preload} autoPlay={false}
                     height={height} width={width} poster={poster}>
                 </video>
-                <MFileBody {...this.props} />
+                <MFileBody {...this.props} decryptedUrl={this.state.decryptedUrl} />
             </span>
         );
     },