Using Html/Javascript you can only select files using the file upload html component (I think Flash / Silverlight wrap this to make things easier but its still sandboxed)
You can however use Java Applets (orwhatever they are called these days), Native ActiveX controls or .Net Controls to provide additional functionality (this hase security implications and required VM/Runtimes Frameworks etc)
Adobe Air or other client side technology might work, but looks like you want to do this in JavaScript. In this case, uploading the file to the server and manipulating from there is the best bet.
Unfortunately in some browsers isn't such functionality built in therefore it is necessary to use some tricks or extensions. As well as it is necessary to differentiate between HTML5 and Flash video.
Chrome
HTML5
Such functionality will be built-in the Chrome since January 2018, now following can be used:
Disable HTML5 autoplay extension
https://chrome.google.com/webstore/detail/disable-html5-autoplay/efdhoaa...
Flash videos
In the Chrome menu, go to settings and scroll down to Show Advanced Settings. Click this and under the Privacy heading, click Content Settings. In the pop-up window, scroll down to Plug-ins and select the Click to play radio button.
Firefox
HTML5
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.
(2) In the search box above the list, type or paste media*play and pause while the list is filtered
(3) To delay media from auto-starting in background tabs, I suggest: double-click the media.block-play-until-visible preference to switch the value from false to true
(4) To prevent media from auto-starting in any tabs: double-click the media.autoplay.enabled preference to switch the value from true to false
Flash videos
Flashstopper extension
https://addons.mozilla.org/cs/firefox/addon/flashstopper/
Opera
HTML5
Disable HTML5 Autoplay extension
https://addons.opera.com/en/extensions/details/disable-html5-autoplay/?d...
Flash videos
Use same approach as for Flash videos in Chrome (see above)
In addition to another solution to this problem mentioning the usage of various ad blocking software in the form of browser plug-ins, I would recommend a different approach:
Block Flash-elements. Flash is a shitty format mostly used by advertisers. Blocking it helped me not only against advertisements, but also with increasing the battery life of my computer.
An appropriate software for this would be Clicktoflash (http://clicktoflash.com) - it has the advantage of still offering you the blocked flash-applet if you want to see it, as it might be the case with designerly websites or stream video players. There are similar programs for other browsers.
While creating the flash-file you have to define the export-options. Those can be found at file – publishing options, like the size or quality of the film. When integrating a text in the flash-file, the text options have to be defined separately. There exist the options of using the computer fonts. You just have to set a mark at the options while the text is selected. The flash-file itself has to be embedded in html like this: <object classid="clsid:d27cdb6e-ae6d-11cf-96b8-444553540000" codebase="http://fpdownload.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#ve..." width="550" height="400" id="test" align="middle"><param name="allowScriptAccess" value="sameDomain" /><param name="movie" value="test.swf" /><param name="quality" value="high" /><param name="bgcolor" value="#ffffff" /><embed src="test.swf" quality="high" bgcolor="#ffffff" width="550" height="400" name="test" align="middle" allowScriptAccess="sameDomain" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" /></object> With the parameters you can also change the backgroundcolour or quality after exporting the swf-file.