HTML5视频的字节范围请求(伪流)如何工作?

If you play an HTML5 video for a video that is hosted on a server that accepts range requests, then when you try to seek ahead to a non-buffered part of the video you'll notice from the network traffic that the browser makes a byte range-request. I'm assuming that the browser computes the byte by knowing the total video size ahead of time and assuming a constant bitrate (if you click half-way in the progress bar, then it will request the byte at the half-way point). But especially if the video is variable bitrate, it seems unlikely that the byte it requests could really correspond to the time-point that the user clicked on, and the byte would likely fall in the middle of a frame.If you play an HTML5 video for a video that is