UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36

Example URL:
http://output.jsbin.com/niwelo

Steps to reproduce the problem:
1. visit http://output.jsbin.com/niwelo
2. click on the play button of the video

What is the expected behavior?
Should start playing almost immediately. (my ADSL's real speed tested at http://www.speedtest.net/ is about 14Mbps)

The video bitrate is not very high, and 1MB or less should be enough to fill a reasonable buffer. You shouldn't need to wait to download much more than that in order to start playing

What went wrong?
Playback does not start until about 4Mb are downloaded, which is about 30 seconds worth of video, and it takes several seconds.

Note that the seekbar shows the portion of video already downloaded while playing, and you can see that once playback starts, it remains the same for a very long time. That is, it doesn't download an additional chunk of video until you get pretty close to the end of the already downloaded portion. This is expected, but it proves that the buffer is already full long before playback starts, so there is no valid reason for waiting that much to start playing.

By inspecting the Network tab in DevTools, it appears that the chunk that "has to" be downloaded before playback start is exactly the one that is requested with the first request. I don't know why you request such a big chunk on the first request, but regardless of that, there's absolutely no need to wait for the first request to complete to start playback.

It's unbelievable that something so trivial as video playback is so broken.

Did this work before? N/A 

Is it a problem with Flash or HTML5? HTML5

Does this work in other browsers? Yes 

Chrome version: 51.0.2704.106  Channel: stable
OS Version: 
Flash Version: Shockwave Flash 22.0 r0

Note that Firefox does it right.