jQuery, why the rewind playbackRate doesn't work?

问题:

I got the fast forward playbackRate work fine. Now I try with the rewind part with negative number but it doesn't work. The w3school say to use negative number to rewind it. http://www.w3schools.com/tags/av_prop_playbackrate.asp Anyone can tell me what I did wrong?

Here my javascript worked code for fast forward,

$("#speed").click(function() { // button function for 3x fast speed forward     video.playbackRate = 3.0; }); 

Then here not success rewind code,

$("#negative").click(function() { // button function for rewind     video.playbackRate = -3.0; }); 

回答1:

Sample Fiddle

Doesn't look like there is complete browser support for the playback rate option as far as rewind is concerned. You can fake it by using setinterval and subtracting the currentTime of the video.

var video = document.getElementById('video'); var intervalRewind; $(video).on('play',function(){     video.playbackRate = 1.0;     clearInterval(intervalRewind); }); $(video).on('pause',function(){     video.playbackRate = 1.0;     clearInterval(intervalRewind); }); $("#speed").click(function() { // button function for 3x fast speed forward     video.playbackRate = 3.0; }); $("#negative").click(function() { // button function for rewind    intervalRewind = setInterval(function(){        video.playbackRate = 1.0;        if(video.currentTime == 0){            clearInterval(intervalRewind);            video.pause();        }        else{            video.currentTime += -.1;        }             },30); }); 

I also added some extra listeners for the play and pause button to clear the interval. Might want to look into doing some toggling feature on the fast foward and rewind buttons as well.

回答2:

• Make sure you test in a supported browser. I only found it to work on IE10 (though it's quite sloppy)

• Trying to set a negative value in IE9 causes the video to pause (sets it to 0)

• It's supposed to work in chrome according to w3schools, but I haven't had luck there

• Should work on Safari too, though I haven't tested

  example

回答3:

This is, yet another, example of w3school.com providing false information. They forgot to point out that:

When the element has a current media controller, the playbackRate attribute is ignored and the current media controller's playbackRate is used instead.

Source: http://www.w3.org/TR/html5/embedded-content-0.html#playing-the-media-resource

After some testing using this demo, it turns out, when the media controller is present, playbackRate must be greater than or equal to 0. If video.playbackRate < 0, it simply won't play.

This means you cannot "rewind" using playbackRate when the media controller is present. However, you can rewind the video by doing something like :

var _el = document.getElementById("video");  _el.currentTime -= 5; 

DEMO: http://jsfiddle.net/dirtyd77/sZVAq/3/

or

<button onclick='video.currentTime-=5'>Rewind</button>

DEMO: http://jsfiddle.net/dirtyd77/sZVAq/2/

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