如何检测 HTML5 视频是否已暂停缓冲？

Question

我正在尝试测试视频是否断断续续。我注意到当视频暂停缓冲时不会触发pause 事件。检测视频是否已暂停缓冲的最佳方法是什么？

Answer 1

我通过每 x 毫秒检查玩家进度来做到这一点，例如50. 如果玩家没有达到预期的进步，那么我们正在缓冲。这是相当可靠的，因为我发现在视频缓冲的所有情况下都不会触发其他事件，例如 waiting 或 stalled。

请注意，间隔必须大于预期的帧间差异，但我相信您无论如何都不会想要那么精确。考虑到人类很可能无法感知该区域的差异，估计在 ±300 毫秒内的缓冲时间仍然可以。

检查用户是否没有主动暂停播放很重要。

var checkInterval  = 50.0 // check every 50 ms (do not use lower values)
var lastPlayPos    = 0
var currentPlayPos = 0
var bufferingDetected = false
var player = document.getElementById('videoPlayer')

setInterval(checkBuffering, checkInterval)
function checkBuffering() {
    currentPlayPos = player.currentTime

    // checking offset should be at most the check interval
    // but allow for some margin
    var offset = (checkInterval - 20) / 1000

    // if no buffering is currently detected,
    // and the position does not seem to increase
    // and the player isn't manually paused...
    if (
            !bufferingDetected 
            && currentPlayPos < (lastPlayPos + offset)
            && !player.paused
        ) {
        console.log("buffering")
        bufferingDetected = true
    }

    // if we were buffering but the player has advanced,
    // then there is no buffering
    if (
        bufferingDetected 
        && currentPlayPos > (lastPlayPos + offset)
        && !player.paused
        ) {
        console.log("not buffering anymore")
        bufferingDetected = false
    }
    lastPlayPos = currentPlayPos
}

Answer 2

您要查找的事件是waiting。

来自spec：

一个等待的 DOM 事件可以作为一个元素的结果被触发 由于其 readyState 属性，可能正在播放停止播放 更改为低于 HAVE_FUTURE_DATA 的值。

paused 状态不会改变，因为视频仍在“可能播放”（即“正在尝试”播放）。所以waiting 事件触发。当加载足够的数据时，playing 会触发。

您还可以通过查看networkState 和readyState 两个属性随时检查状态

if (video.networkState === video.NETWORK_LOADING) {
    // The user agent is actively trying to download data.
}

if (video.readyState < video.HAVE_FUTURE_DATA) {
    // There is not enough data to keep playing from this point
}

Answer 3

您可以只检查缓冲的视频内容长度，如果它小于当前播放部分，则只需触发暂停事件。使用以下代码，您可以检查缓冲的视频长度。

$vid = $("#video_id");

$vid.on('progress', function(e) {

    percentVidLoaded = null;
    // FF4+, Chrome
    if ($vid[0] && $vid[0].buffered && $vid[0].buffered.length > 0 && $vid[0].buffered.end && $vid[0].duration) {
        percentVidLoaded = $vid[0].buffered.end(0) / $vid[0].duration;
    }
    /* Some browsers (e.g., FF3.6 and Safari 5) cannot calculate target.bufferered.end()
     *  to be anything other than 0. If the byte count is available we use this instead.
     *  Browsers that support the else if do not seem to have the bufferedBytes value and
     *  should skip to there.
     */
    else if ($vid[0] && $vid[0].bytesTotal != undefined && $vid[0].bytesTotal > 0 && $vid[0].bufferedBytes != undefined) {
        percentVidLoaded = $vid[0].bufferedBytes / $vid[0].bytesTotal;
    }
    if (percentVidLoaded !== null) {
        percentVidLoaded = 100 * Math.min(1, Math.max(0, percentVidLoaded));
    }
});

Answer 4

根据 MDN 文档的“等待”事件是 -

当请求的操作（例如播放）延迟等待另一个操作（例如搜索）完成时发送。

所以搜索或网络请求将触发“等待”。 cmets 中的迈克尔确实指出，截至 2019 年，“等待”是可靠的，所以我试了一下，它奏效了！

let slowInternetTimeout = null;

let threshold = 3000; //ms after which user perceives buffering

video.addEventListener('waiting', () => {
    slowInternetTimeout = setTimeout(() => {
        //show buffering
    }, threshold);
});
video.addEventListener('playing', () => {
    if(slowInternetTimeout != null){
        clearTimeout(slowInternetTimeout);
        slowInternetTimeout = null;
    }
});

Answer 5

您需要检查缓冲区是否小于当前视频时间。如果是这样，则视频正在缓冲。但是，您应该以较小的容差进行检查，以确保在确实需要缓冲之前检测到它。

例子：

var video = document.getElementById("myVideo");
var prevBuffer = {
    "buffer": null,
    "time": null
};
var isBuffering = function(){

    if(video && video.buffered && video.buffered.end && video.buffered.length > 0){
        var buffer = video.buffered.end(0);
        var time   = video.currentTime;

        // Check if the video hangs because of issues with e.g. performance
        if(prevBuffer.buffer === buffer && prevBuffer.time === time && !video.paused){
            return true;
        }
        prevBuffer = {
            "buffer": buffer,
            "time": time
        };
        // Check if video buffer is less
        // than current time (tolerance 3 sec)
        if((buffer - 3) < time){
            return true;
        }
    }
    return false;

};
video.addEventListener("play", function(e){
    // Make sure this handler is only called once
    e.target.removeEventListener(e.type, arguments.callee);
    // Give browsers 3secs time to buffer
    setTimeout(function(){
        // As "progress", "stalled" or "waiting" aren't fired
        // reliable, we need to use an interval
        var interval = setInterval(function(){
            if(isBuffering()){
                clearInterval(interval);
                console.log("Buffering");
            }
        }, 500);
    }, 3000);
});