With pseudo-streaming "standards" for flash (which doesn't allow HTTP Range header), the common approach is to send a GET param (like start=123) to emulate seek in videos. Then backend servers use this parameter, to split the MP4 file - rewrite header, and send the (shrunken) file to client.

Currently, there's a limited amount of options to do this, without installing a module to the webserver itself (E.G CodeShop's H264 Streaming Module - open sourced under CC 3.0 license). This is not suitable in environments where you don't control the webserver. Having this functionality in PHP would allow any user to video enable their site, and have support for seek using a flash player - without patching any webserver.

I believe that having the above functionality would help increase the footprint of the library, as this is a much sought after feature.

I know the name 'php-reader' is slightly off, in terms of this item - but from what I can tell, there's a number of write operations already implemented for most boxes? Not to mention Zend_Io is bundled in there as well - which does fully support write operations.