JavaCV FrameGrabber問題彙總

@Date 2018.09.27

FrameGrabber類

• JavaCV中FrameGrabber類可以連接配接直播流位址, 進行解碼, 擷取Frame幀資訊, 常用方式如下

FrameGrabber grabber = new FrameGrabber("rtsp:/192.168.0.0");
while(true) {
    Frame frame = grabber.grabImage();
    // ...
}
           

問題(1)

• 在如上代碼中, 若直播位址網絡不通, 或者連接配接逾時, 則會出現程式Hang住的情況, 也就是同步阻塞卡死. 因為可以增加一個逾時參數進行解決.

解決辦法(1)

FrameGrabber grabber = new FrameGrabber("rtsp:/192.168.0.0");
// 增加逾時參數
grabber.setOption(TimeoutOption.STIMEOUT.key(), "5000000");
while(true) {
    Frame frame = grabber.grabImage();
    // ...
}

           

問題(2)

• FrameGrabber hangs when server connection is broken
• 在問題(1)的基礎上, 若剛開始網絡是通的, 程式可以擷取到解碼後的視訊幀. 而在已經運作通了的時候, 網絡突然斷掉, 此時上面的timeout是不生效的.
• 同時可以參考GitHub上的提問( https://github.com/bytedeco/javacv/issues/1063 )

解決辦法(2)

• 在GitHub上面, 作者介紹了Callback_Pointer方式, 參考( https://github.com/bytedeco/javacv/blob/master/samples/FFmpegStreamingTimeout.java
• 但是經過測試, 發現此方式還是不能解決問題(2), 在FrameGrabber外部增加callback對原類中的對象不生效.
• 故使用一種笨方式, 繼承重寫FrameGrabber類, 把逾時callback增加到原代碼邏輯中.

public class CustomFrameGrabber extends FrameGrabber {
    /**
     * 讀流逾時時間 : 10秒
     */
    private static final int FRAME_READ_TIMEOUT = 10000;

    // 增加callbacjk 監聽
    private final AtomicLong lastFrameTime = new AtomicLong(System.currentTimeMillis());
    private final AVIOInterruptCB.Callback_Pointer cp = new avformat.AVIOInterruptCB.Callback_Pointer() {
        @Override
        public int call(Pointer pointer) {
            // 0:continue, 1:exit
            if (lastFrameTime.get() + FRAME_READ_TIMEOUT < System.currentTimeMillis()) {
                MONITOR_LOGGER.warn("frame read timeout 10s.");
                return 1;
            }
            return 0;
        }
    };
    
    // ... 省略中間代碼
    
    void startUnsafe() throws Exception {
        int ret;
        img_convert_ctx = null;
        oc = new AVFormatContext(null);
        video_c = null;
        audio_c = null;
        pkt = new AVPacket();
        pkt2 = new AVPacket();
        sizeof_pkt = pkt.sizeof();
        got_frame = new int[1];
        frameGrabbed = false;
        frame = new Frame();
        timestamp = 0;
        frameNumber = 0;

        pkt2.size(0);

        // Open video file
        AVInputFormat f = null;
        if (format != null && format.length() > 0) {
            if ((f = av_find_input_format(format)) == null) {
                throw new Exception("av_find_input_format() error: Could not find input format \"" + format + "\".");
            }
        }
        AVDictionary options = new AVDictionary(null);
        if (frameRate > 0) {
            AVRational r = av_d2q(frameRate, 1001000);
            av_dict_set(options, "framerate", r.num() + "/" + r.den(), 0);
        }
        if (pixelFormat >= 0) {
            av_dict_set(options, "pixel_format", av_get_pix_fmt_name(pixelFormat).getString(), 0);
        } else if (imageMode != ImageMode.RAW) {
            av_dict_set(options, "pixel_format", imageMode == ImageMode.COLOR ? "bgr24" : "gray8", 0);
        }
        if (imageWidth > 0 && imageHeight > 0) {
            av_dict_set(options, "video_size", imageWidth + "x" + imageHeight, 0);
        }
        if (sampleRate > 0) {
            av_dict_set(options, "sample_rate", "" + sampleRate, 0);
        }
        if (audioChannels > 0) {
            av_dict_set(options, "channels", "" + audioChannels, 0);
        }
        for (Entry<String, String> e : this.options.entrySet()) {
            av_dict_set(options, e.getKey(), e.getValue(), 0);
        }
        if (inputStream != null) {
            if (readCallback == null) {
                readCallback = new CustomFFmpegFrameGrabber.ReadCallback();
            }
            if (seekCallback == null) {
                seekCallback = new CustomFFmpegFrameGrabber.SeekCallback();
            }
            if (!inputStream.markSupported()) {
                inputStream = new BufferedInputStream(inputStream, 1024 * 1024);
            }
            inputStream.mark(1024 * 1024);
            oc = avformat_alloc_context();
            avio = avio_alloc_context(new BytePointer(av_malloc(4096)), 4096, 0, oc, readCallback, null, seekCallback);
            oc.pb(avio);

            filename = inputStream.toString();
            inputStreams.put(oc, inputStream);
        }
        // 2018.09.07 add 此處一行為新增代碼, 意思是每次取到幀時, 都更新一下時間. 若遇到網絡斷開, hang住時, 則可用此時間判斷逾時
        lastFrameTime.set(System.currentTimeMillis());
        oc = avformat_alloc_context();
        avformat.AVIOInterruptCB cb = new avformat.AVIOInterruptCB();
        cb.callback(cp);
        oc.interrupt_callback(cb);
        // 省略後續代碼...
    }
    
    public Frame grabFrame(boolean doAudio, boolean doVideo, boolean processImage, boolean keyFrames) throws Exception {
        if (oc == null || oc.isNull()) {
            throw new Exception("Could not grab: No AVFormatContext. (Has start() been called?)");
        } else if ((!doVideo || video_st == null) && (!doAudio || audio_st == null)) {
            return null;
        }
        // 2018.09.07 add 擷取幀時, 更新最新時間戳
        lastFrameTime.set(System.currentTimeMillis());
        
        // 省略後續代碼...
    }
}