In AS3 while using NetStream for video playback how do I seek when I use appendBytes

问题

I am trying to use NetStream to play from a byteArray. Please see this for what I am talking about.

I am able to get this to play the video. However now I need to be able to see to a particular second. I am not able to do this. If I go through the bytearray I know I can get the metadata and the keyframes as required and the offset ( in bytes) as to where each keyframe is at. However there is no way to seek to a particular offset. It only supports seek in seconds and that doesn't seem to work on the byteArray.

How do I go about this ?

回答1:

I got I worked:

// onmetadata function get all timestamp and corresponding fileposition..

function onMetaData(infoObject: Object): void {

    for (var propName: String in infoObject) {

        if (propName == "keyframes") {
            var kfObject: Object = infoObject[propName];
            var timeArr: Array = kfObject["times"];
            var byteArr: Array = kfObject["filepositions"];

            for (var i: int = 0;i < timeArr.length;i++) {
                var tagPos: int = byteArr[i]; //Read the tag size;
                var timestamp: Number = timeArr[i]; //read the timestamp;
                tags.push({
                    timestamp: timestamp,
                    tagPos: tagPos
                });

            }
        }

// onseek click get approximate timestamp and its fileposition
protected

function seek_click(seektime: Number): void {

    var cTime: Number = 0;
    var pTime: Number = 0;

    for (var i: int = 1;i < tags.length;i++) {
        cTime = tags[i].timestamp;
        pTime = tags[i - 1].timestamp;

        if (pTime < seektime) {
            if (seektime < cTime) {
                seekPos = tags[i - 1].tagPos;
                stream.seek(pTime);
                break;
            }
        }
    }
}

/// append bytes on seekposition
private

function netStatusHandler(event: NetStatusEvent): void {

    switch (event.info.code) {

    case "NetStream.Seek.Notify":
        stream.appendBytesAction(NetStreamAppendBytesAction.RESET_SEEK);

        totalByteArray.position = seekPos;

        var bytes: ByteArray = new ByteArray();
        totalByteArray.readBytes(bytes);
        stream.appendBytes(bytes);

        stream.resume();
        break;
    }
}

回答2:

Each flv tag has a timestamp and offset. You can find the FLV spec here: http://download.macromedia.com/f4v/video_file_format_spec_v10_1.pdf

You can't play the video at any position. You must start at the beginning of a tag so you will need to find the tag with a time nearest to the time you want to seek to.

Your going to want to do something like this:

private var tags:Array = [];
private var fileStream:FileStream;  
private var netStream:NetStream;
private var seekTime:Number;

public function function readTags(path:String):void
{
    //open the fileStream for reading

    while(fileStream.bytesAvailable > 0)
    {
        //sudo code for reading the tags of an FLV

        var tagPosition:int = fileStream.position;
        var tagSize:int = //Read the tag size;
        var timestamp:int = //read the timestamp;
        tags.push({timestamp:timestamp, position:tagPosition}];
        fileStream.position += tagSize;  //goto the next tag
    }
}

private function findTagPosition(timeInMilliseconds:int):int
{
    //Search the tags array for the tags[a].timestamp that is nearest to timeInMilliseconds

    return tags[indexOfTagNearstToTimeInMilliseconds].position;
}

public function seek(time:Number):void
{
    seektime = time;
    netStream.seak(time);
}

private function onNetStatusEvent(event:NetStatusEvent):void
{
    if(event.info.code == NetStreamCodes.NETSTREAM_SEEK_NOTIFY)
    {
        fileStream.position = findTagPosition(seekTime * 1000);
        netStream.appendBytesAction(NetStreamAppendBytesAction.RESET_SEEK);
        var bytes:ByteArray = new ByteArray();
        fileStream.readBytes(bytes);
        netStream.appendBytes(bytes);
    }
}

回答3:

Try my code posted here for an example of how seeking is done without needing "keyframes" to exist in FLV metadata etc. There is also a working demo available to test (use FLV with H264 and AAC/MP3 audio).

That code was partly to answer this question (if you need additional info/context)

来源：https://stackoverflow.com/questions/3825103/in-as3-while-using-netstream-for-video-playback-how-do-i-seek-when-i-use-appendb

标签

actionscript-3

flv

netstream