LSWS want to have PHP run as fast as possible. however, if the result of PHP processing was discarded, it will causes some waste in resource.
There is no good solution on LSWS side, as PHP run out of LSWS process only connected with a socket connection.
I am not sure your code fetch the whole content back then start the play back? or start play back as early as data is available.
If it is the former. you need to change your code, it is too inefficient for large media file.
If it is the later case, you can apply some bandwidth throttling policy in PHP, say, fetch the first xxxKB as fast as it can, then thottle it at certain bandwidth cap like 100KB/s, which is just a little bit faster than bandwidth need to play the video smoothly.
LSWS buffer the response, you cannot rely on LSWS to cap the bandwidth for PHP.