Android使用FFMpeg实现推送视频直播流到服务器

背景

在过去的2015年中，视频直播页的新宠无疑是户外直播。随着4G网络的普及和覆盖率的提升，主播可以在户外通过手机进行直播。而观众也愿意为这种可以足不出户而观天下事的服务买单。基于这样的背景，本文主要实现在Android设备上采集视频并推流到服务器。

概览

如下图所示，在安卓上采集并推流主要应用到两个类。首先是安卓Api自带的Camera，实现从摄像头采集图像。然后是Javacv 中的FFMpegFrameRecorder类实现对Camera采集到的帧编码并推流。

关键步骤与代码

下面结合上面的流程图给出视频采集的关键步骤。 首先是Camera类的初始化。

// 初始化Camera设备
cameraDevice = Camera.open();
     Log.i(LOG_TAG, "cameara open");
     cameraView = new CameraView(this, cameraDevice);

上面的CameraView类是我们实现的负责预览视频采集和将采集到的帧写入FFMpegFrameRecorder的类。具体代码如下：

class CameraView extends SurfaceView implements SurfaceHolder.Callback, PreviewCallback {

    private SurfaceHolder mHolder;
    private Camera mCamera;

    public CameraView(Context context, Camera camera) {
        super(context);
        Log.w("camera", "camera view");
        mCamera = camera;
        mHolder = getHolder();
        //设置SurfaceView 的SurfaceHolder的回调函数
        mHolder.addCallback(CameraView.this);
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
        //设置Camera预览的回调函数
        mCamera.setPreviewCallback(CameraView.this);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        try {
            stopPreview();
            mCamera.setPreviewDisplay(holder);
        } catch (IOException exception) {
            mCamera.release();
            mCamera = null;
        }
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        stopPreview();

        Camera.Parameters camParams = mCamera.getParameters();
        List<Camera.Size> sizes = camParams.getSupportedPreviewSizes();
        // Sort the list in ascending order
        Collections.sort(sizes, new Comparator<Camera.Size>() {

            public int compare(final Camera.Size a, final Camera.Size b) {
                return a.width * a.height - b.width * b.height;
            }
        });

        // Pick the first preview size that is equal or bigger, or pick the last (biggest) option if we cannot
        // reach the initial settings of imageWidth/imageHeight.
        for (int i = 0; i < sizes.size(); i++) {
            if ((sizes.get(i).width >= imageWidth && sizes.get(i).height >= imageHeight) || i == sizes.size() - 1) {
                imageWidth = sizes.get(i).width;
                imageHeight = sizes.get(i).height;
                Log.v(LOG_TAG, "Changed to supported resolution: " + imageWidth + "x" + imageHeight);
                break;
            }
        }
        camParams.setPreviewSize(imageWidth, imageHeight);

        Log.v(LOG_TAG, "Setting imageWidth: " + imageWidth + " imageHeight: " + imageHeight + " frameRate: " + frameRate);

        camParams.setPreviewFrameRate(frameRate);
        Log.v(LOG_TAG, "Preview Framerate: " + camParams.getPreviewFrameRate());

        mCamera.setParameters(camParams);

        // Set the holder (which might have changed) again
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.setPreviewCallback(CameraView.this);
            startPreview();
        } catch (Exception e) {
            Log.e(LOG_TAG, "Could not set preview display in surfaceChanged");
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        try {
            mHolder.addCallback(null);
            mCamera.setPreviewCallback(null);
        } catch (RuntimeException e) {
            // The camera has probably just been released, ignore.
        }
    }

    public void startPreview() {
        if (!isPreviewOn && mCamera != null) {
            isPreviewOn = true;
            mCamera.startPreview();
        }
    }

    public void stopPreview() {
        if (isPreviewOn && mCamera != null) {
            isPreviewOn = false;
            mCamera.stopPreview();
        }
    }

    @Override
    public void onPreviewFrame(byte[] data, Camera camera) {
        if (audioRecord == null || audioRecord.getRecordingState() != AudioRecord.RECORDSTATE_RECORDING) {
            startTime = System.currentTimeMillis();
            return;
        }
        //如果是录播，则把该帧先存在内存中
        if (RECORD_LENGTH > 0) {
            int i = imagesIndex++ % images.length;
            yuvImage = images[i];
            timestamps[i] = 1000 * (System.currentTimeMillis() - startTime);
        }
        if (yuvImage != null && recording) {
            ((ByteBuffer) yuvImage.image[0].position(0)).put(data);
			//如果是直播则直接写入到FFmpegFrameRecorder中
            if (RECORD_LENGTH <= 0) try {
                Log.v(LOG_TAG, "Writing Frame");
                long t = 1000 * (System.currentTimeMillis() - startTime);
                if (t > recorder.getTimestamp()) {
                    recorder.setTimestamp(t);
                }
                recorder.record(yuvImage);
            } catch (FFmpegFrameRecorder.Exception e) {
                Log.v(LOG_TAG, e.getMessage());
                e.printStackTrace();
            }
        }
    }
}

初始化FFmpegFrameRecorder类

    recorder = new FFmpegFrameRecorder(ffmpeg_link, imageWidth, imageHeight, 1);
    //设置视频编码  28 指代h.264
    recorder.setVideoCodec(28);
    recorder.setFormat("flv");
    //设置采样频率
    recorder.setSampleRate(sampleAudioRateInHz);
    // 设置帧率，即每秒的图像数
    recorder.setFrameRate(frameRate);
    //音频采集线程
	audioRecordRunnable = new AudioRecordRunnable();
    audioThread = new Thread(audioRecordRunnable);
    runAudioThread = true;

其中的AudioRecordRunnable是我们自己实现的音频采集线程，代码如下

 class AudioRecordRunnable implements Runnable {

    @Override
    public void run() {
        android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_URGENT_AUDIO);

        // Audio
        int bufferSize;
        ShortBuffer audioData;
        int bufferReadResult;

        bufferSize = AudioRecord.getMinBufferSize(sampleAudioRateInHz,
                AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
        audioRecord = new AudioRecord(MediaRecorder.AudioSource.MIC, sampleAudioRateInHz,
                AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, bufferSize);
		//如果是录播，则需要录播长度的缓存
        if (RECORD_LENGTH > 0) {
            samplesIndex = 0;
            samples = new ShortBuffer[RECORD_LENGTH * sampleAudioRateInHz * 2 / bufferSize + 1];
            for (int i = 0; i < samples.length; i++) {
                samples[i] = ShortBuffer.allocate(bufferSize);
            }
        } else {
        //直播只需要相当于一帧的音频的数据缓存
            audioData = ShortBuffer.allocate(bufferSize);
        }

        Log.d(LOG_TAG, "audioRecord.startRecording()");
        audioRecord.startRecording();

        /* ffmpeg_audio encoding loop */
        while (runAudioThread) {
            if (RECORD_LENGTH > 0) {
                audioData = samples[samplesIndex++ % samples.length];
                audioData.position(0).limit(0);
            }
            //Log.v(LOG_TAG,"recording? " + recording);
            bufferReadResult = audioRecord.read(audioData.array(), 0, audioData.capacity());
            audioData.limit(bufferReadResult);
            if (bufferReadResult > 0) {
                Log.v(LOG_TAG, "bufferReadResult: " + bufferReadResult);
                // If "recording" isn't true when start this thread, it never get's set according to this if statement...!!!
                // Why?  Good question...
                if (recording) {
               		//如果是直播，则直接调用recordSamples 将音频写入Recorder
                    if (RECORD_LENGTH <= 0) try {
                        recorder.recordSamples(audioData);
                        //Log.v(LOG_TAG,"recording " + 1024*i + " to " + 1024*i+1024);
                    } catch (FFmpegFrameRecorder.Exception e) {
                        Log.v(LOG_TAG, e.getMessage());
                        e.printStackTrace();
                    }
                }
            }
        }
        Log.v(LOG_TAG, "AudioThread Finished, release audioRecord");

        /* encoding finish, release recorder */
        if (audioRecord != null) {
            audioRecord.stop();
            audioRecord.release();
            audioRecord = null;
            Log.v(LOG_TAG, "audioRecord released");
        }
    }
}

接下来是开始直播和停止直播的方法

//开始直播
public void startRecording() {

    initRecorder();

    try {
        recorder.start();
        startTime = System.currentTimeMillis();
        recording = true;
        audioThread.start();

    } catch (FFmpegFrameRecorder.Exception e) {
        e.printStackTrace();
    }
}

public void stopRecording() {
	//停止音频线程
    runAudioThread = false;
    try {
        audioThread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    audioRecordRunnable = null;
    audioThread = null;

    if (recorder != null && recording) {
    //如果是录播，则将缓存中的帧加上时间戳后写入
        if (RECORD_LENGTH > 0) {
            Log.v(LOG_TAG, "Writing frames");
            try {
                int firstIndex = imagesIndex % samples.length;
                int lastIndex = (imagesIndex - 1) % images.length;
                if (imagesIndex <= images.length) {
                    firstIndex = 0;
                    lastIndex = imagesIndex - 1;
                }
                if ((startTime = timestamps[lastIndex] - RECORD_LENGTH * 1000000L) < 0) {
                    startTime = 0;
                }
                if (lastIndex < firstIndex) {
                    lastIndex += images.length;
                }
                for (int i = firstIndex; i <= lastIndex; i++) {
                    long t = timestamps[i % timestamps.length] - startTime;
                    if (t >= 0) {
                        if (t > recorder.getTimestamp()) {
                            recorder.setTimestamp(t);
                        }
                        recorder.record(images[i % images.length]);
                    }
                }

                firstIndex = samplesIndex % samples.length;
                lastIndex = (samplesIndex - 1) % samples.length;
                if (samplesIndex <= samples.length) {
                    firstIndex = 0;
                    lastIndex = samplesIndex - 1;
                }
                if (lastIndex < firstIndex) {
                    lastIndex += samples.length;
                }
                for (int i = firstIndex; i <= lastIndex; i++) {
                    recorder.recordSamples(samples[i % samples.length]);
                }
            } catch (FFmpegFrameRecorder.Exception e) {
                Log.v(LOG_TAG, e.getMessage());
                e.printStackTrace();
            }
        }

        recording = false;
        Log.v(LOG_TAG, "Finishing recording, calling stop and release on recorder");
        try {
            recorder.stop();
            recorder.release();
        } catch (FFmpegFrameRecorder.Exception e) {
            e.printStackTrace();
        }
        recorder = null;

    }
}

以上即为关键的步骤和代码，下面给出完整项目地址 RtmpRecorder

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