I use your last version of the allvideos plugin, with Joomla 3.4.8.
I have created a video in ogv format, and it works fine with a video reader on Linux Ubuntu.
I put the file in the right library like I define it in the parameters of the plugin.
I write an article within the commands :
{jcomments on}
{ogv}filename{/ogv}

and the result on my screen is :

filename{/ogv}
well followed by the block for a new comment.

ps : I use some other plugins but without any problem

Thanks for your help !

And the result is the same on my screen if i write only the command of the video plugin (without the jcomments command, juste written here to show that others plugins work finely).
I have tried also to install your product called "allvideos-master" : none problem for installing it, but he result isn't better (exactly the same, even after the right cleaning of the caches).

I have found a solution with that script into my Joomla article :

{source}

<p>
<video controls="controls" width="350" height="260">
<source src="images/videos/filename.ogv" type="video/ogg" />
</video>
</p>

{/source}

ps : but neither the script {ogv}filename{/ogv} nor the script {ogg}filename{/ogg} runs fine

@Claude Lendrevie

Ensure that you have not added any HTML markup inside the video tag. Use the view source button of your WYSIWYG editor to ensure there is no markup inserted there.