For those that didn’t have a Pi with a camera at hand, I also wrote an emulated camera driver that streams a sequence of jpeg images stored on disk. One aspect of the original streaming server that people did not like is that the background thread that captures video frames from the Raspberry Pi camera starts when the first client connects to the stream, but then it never stops. A more efficient way to handle this background thread is to only have it running while there are viewers, so that the camera can be turned off when nobody is connected. Here the –worker-class gevent option configures Gunicorn to use the gevent framework (you must install it with pip install gevent). The eventlet and gevent workers in Gunicorn allocate a thousand concurrent clients by default, so that should be much more than what a server of this kind is able to support anyway.

The –threads 5 option tells Gunicorn to handle at most five concurrent requests. That means that with this number you can get up to five clients to watch the stream simultaneously. The –workers 1 options limits the server to a single process. This is required because only one process can connect restful api python flask to a camera to capture frames. This new version of the Raspberry Pi’s camera thread has been made generic with the use of yet another generator. The thread expects the frames() method (which is a static method) to be a generator implemented in subclasses that are specific to different cameras.

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The generators can then block while they wait for the signal before they deliver the next frame. In looking through synchronization primitives, I’ve found that threading.Event is the one that matches this behavior. So basically, each generator should have an event object, and then the camera thread should signal all the active event objects to inform all the running generators when a new frame is available. The generators deliver the frame and reset their event objects, and then go back to wait on them again for the next frame.

It’s our mission to provide every college student, weekend warrior, and others of legal drinking age in the Free World with the best flask money can buy. A common problem that a lot of people mentioned to me is that it is hard to add support for other cameras. The Camera class that I implemented for the Raspberry Pi is fairly complex because it uses a background capture thread to talk to the camera hardware. That article is extremely popular, but not because it teaches how to implement streaming responses, but because a lot of people want to implement streaming video servers.

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In both cases there was a single client viewing the stream. The OpenCV driver went from about 45% CPU down to 12% for a single client, with each new client adding about 3%. In general it makes sense for the background thread to run as fast as possible, because you want the frame rate to be as high as possible for each client. But you definitely do not want the generator that delivers frames to a client to ever run at a faster rate than the camera is producing frames, because that would mean duplicate frames will be sent to the client. While these duplicates do not cause any problems, they increase CPU and network usage without any benefit. Another observation that was made a few times is that the server consumes a lot of CPU.

The quality was the same as something I trust on my own little boy, so I can very realistically underscore the value of the material of the Freedom Flask. Obviously, I give mad props to anyone that can create such a crazy idea and go through with its full creation–not everyone takes their ideas to the end stage of production. The agreement that TfL has with London Councils is that the Older Persons Freedom Pass is valid 9am to 4.30am Monday to Friday and all day on weekends and Bank Holidays. London Councils fund all the journeys that are made at those times. ‘ the website boasts, including ‘concerts and festivals, bars and clubs, events with a cash bar, the golf course, movie theatre, the ski sopes’ – and of course – ‘a boring day at the office’. The American-made flask for ‘the rowdy gentleman’ was dreamed up by a University of Georgia graduate tired of trying to sneak beer into sporting events.