Question

I’m scripting with the VLC browser plugin to determine the length of any video file. I first tell VLC to attempt to play the file. Then I periodically probe it for its length. Once it tells me the length is non-zero, I know the video has successfully begun playing and the length is accurate.

The hard part is error detection. I have to detect if the supplied file is a busted video or not even video at all. Someone could lie with a text file incorrectly named as video.avi and VLC wouldn’t be able to play it. I arbitrarily decided that if VLC reports the length as 0 for 5 straight seconds, then I’d consider the supplied file a dud. Is this an accurate assumption? Is it possible that a severely fragmented harddrive would take more then 5 seconds to supply VLC with a video file? Does the bitrate of the file have anything to do with read time?

Below a snippet of my Javascript which determines the file length. You don’t have to read it to understand my question, but some of you might like to see it.

/**
 * Find the total length of a playlist item.
 *
 * @param PlaylistItem playlistItem
 * @param options
 *    onSuccess: void function(int length)
 *    onFailure: void function() - timeout
 *    onComplete: void function() - called after onSuccess or onFailure
 * @return void
 */
findLength: function(playlistItem, options) {
    var option = {
        onSuccess: Prototype.emptyFunction,
        onFailure: Prototype.emptyFunction,
        onComplete: Prototype.emptyFunction
    };

    Object.extend(option, options);

    if (playlistItem.getLength() > 0) {
        option.onSuccess(playlistItem.getLength());
        option.onComplete();
    }

    if (this.lengthPoller) {
        this.lengthPoller.stop();
    }

    this.preview(playlistItem);

    this.lengthPoller = new PeriodicalExecuter(
        function(poller) {
            if (this.secondsInComa >= MYAPP.Vlc.MAX_SECONDS_IN_COMA) {
                this.secondsInComa = 0;
                option.onFailure();
                this.stop();
                poller.stop();
                option.onComplete();
            } else {
                var currLength = this.vlc.input.length;
                if (currLength > 0) {
                    currLength /= 1000;
                    playlistItem.setLength(currLength);
                    option.onSuccess(currLength);
                    this.secondsInComa = 0;
                    this.stop();
                    poller.stop();
                    option.onComplete();
                } else {
                    this.secondsInComa += MYAPP.Vlc.LENGTH_POLLING_PERIOD;
                }
            }
        }.bind(this),
        MYAPP.Vlc.LENGTH_POLLING_PERIOD
    );
}

Answer 1

I found out that it can take greater than 5 seconds. Windows will put a harddrive to sleep if it’s inactive. I tried to load up a video from an inactive drive. It took greater than 5 seconds for the drive to spool up. My code incorrectly marked the video as defective.