Hannes Van De Vreken has posted a tutorial to his site showing users of the Symfony Console component how to show progress on a stream using the ProgressBar helper and a bit of code to inspect the stream itself.
With PHP you can, next to handling HTTP requests, invoke scripts from the command line. [...] The Symfony console component is a very useful tool to define and invoke these kind of CLI tasks. [...] What is actually printed on the console is very important for the issuer of the task. Think of it as the command’s usability. Too little runtime information, the less usable the task. [...] Enter the ProgressBar. The ProgressBar is an output helper that wraps the OutputInterface object.
He talks briefly about how the ProgressBar helper works in the console component's output and gives a simple example of the output. He then shows how to hook it into a bit of PHP using the stream_notification_callback optional parameter (defined in stream_context_create) to point to another class method that handles the progress bar updates. It performs a bit of introspection on the stream and updates the progress as its contents progress. He does point out a few caveats though, including that the transfer is not made asynchronous by this handling.