Android实时直播，一千行java搞定不依赖jni，延迟0.8至3秒，强悍移动端来袭

项目首页：https://github.com/ossrs/srs-sea

SRS服务器项目：https://github.com/ossrs/srs

一个支持RTMP推流的版本：https://github.com/begeekmyfriend/yasea

在Android高版本中，特别是4.1引入了MediaCodec可以对摄像头的图像进行硬件编码，实现直播。

一般Android推流到服务器，使用ffmpeg居多，也就是软编码，实际上使用Android的硬件编码会有更好的体验。

看了下网上的文章也不少，但是都缺乏一个整体跑通的方案，特别是如何推送的服务器。本文把Android推直播流的过程梳理一遍。

AndroidPublisher提出了Android直播的新思路，主要配合SRS服务器完成，优势如下：

使用系统的类，不引入jni和c的库，简单可靠，一千行左右java代码就可以完成。
硬件编码而非软件编码，系统负载低，800kbps编码cpu使用率13%左右。
低延迟和RTMP一样，0.8秒到3秒，使用的协议是HTTP FLV流，原理和RTMP一样。
安装包小无复杂依赖，编译出来的apk都只有1405KB左右。
方便集成，只需要引入一个SrsHttpFlv类，进行转封装和打包发送，可以用在任何app中。

Android直播有几个大的环节：

打开Camera，进行Preview获取YUV图像数据，也就是未压缩的图像。
设置picture和preview大小后，计算YUV的buffer的尺寸，不能简单乘以1.5而应该按照文档计算。
获取YUV的同时，还可以进行预览，只要绑定到SurfaceHolder就可以。
使用MediaCodec和MediaFormat对YUV进行编码，其中MediaCodec是编码，MediaFormat是打包成annexb封装。
设置MediaCodec的colorFormat需要判断是否MediaCodec支持，也就是从MediaCodec获取colorFormat。
将YUV图像，送入MediaCodec的inputBuffer，并获取outputBuffer中已经编码的数据，格式是annexb。
其中queueInputBuffer时，需要指定pts，否则没有编码数据输出，会被丢弃。
将编码的annexb数据，发送到服务器。
一般使用rtmp(librtmp/srslibrtmp/ffmpeg)，因为流媒体服务器的输入一般是rtmp。
若服务器支持http-flv流POST，那么可以直接发送给服务器。

秀一个运行起来的图：

下面是各个重要环节的分解。

YUV图像

第一个环节，打开Camera并预览：

                camera = Camera.open();Camera.Parameters parameters = camera.getParameters();parameters.setFlashMode(Camera.Parameters.FLASH_MODE_OFF);parameters.setWhiteBalance(Camera.Parameters.WHITE_BALANCE_AUTO);parameters.setSceneMode(Camera.Parameters.SCENE_MODE_AUTO);parameters.setFocusMode(Camera.Parameters.FOCUS_MODE_AUTO);parameters.setPreviewFormat(ImageFormat.YV12);Camera.Size size = null;List<Camera.Size> sizes = parameters.getSupportedPictureSizes();for (int i = 0; i < sizes.size(); i++) {//Log.i(TAG, String.format("camera supported picture size %dx%d", sizes.get(i).width, sizes.get(i).height));if (sizes.get(i).width == 640) {size = sizes.get(i);}}parameters.setPictureSize(size.width, size.height);Log.i(TAG, String.format("set the picture size in %dx%d", size.width, size.height));sizes = parameters.getSupportedPreviewSizes();for (int i = 0; i < sizes.size(); i++) {//Log.i(TAG, String.format("camera supported preview size %dx%d", sizes.get(i).width, sizes.get(i).height));if (sizes.get(i).width == 640) {vsize = size = sizes.get(i);}}parameters.setPreviewSize(size.width, size.height);Log.i(TAG, String.format("set the preview size in %dx%d", size.width, size.height));camera.setParameters(parameters);// set the callback and start the preview.buffer = new byte[getYuvBuffer(size.width, size.height)];camera.addCallbackBuffer(buffer);camera.setPreviewCallbackWithBuffer(onYuvFrame);try {camera.setPreviewDisplay(preview.getHolder());} catch (IOException e) {Log.e(TAG, "preview video failed.");e.printStackTrace();return;}Log.i(TAG, String.format("start to preview video in %dx%d, buffer %dB", size.width, size.height, buffer.length));camera.startPreview();

计算YUV的buffer的函数，需要根据文档计算，而不是简单“*3/2”:

    // for the buffer for YV12(android YUV), @see below:// https://developer.android.com/reference/android/hardware/Camera.Parameters.html#setPreviewFormat(int)// https://developer.android.com/reference/android/graphics/ImageFormat.html#YV12private int getYuvBuffer(int width, int height) {// stride = ALIGN(width, 16)int stride = (int)Math.ceil(width / 16.0) * 16;// y_size = stride * heightint y_size = stride * height;// c_stride = ALIGN(stride/2, 16)int c_stride = (int)Math.ceil(width / 32.0) * 16;// c_size = c_stride * height/2int c_size = c_stride * height / 2;// size = y_size + c_size * 2return y_size + c_size * 2;}

图像编码

第二个环节，设置编码器参数，并启动：

                // encoder yuv to 264 es stream.// requires sdk level 16+, Android 4.1, 4.1.1, the JELLY_BEANtry {encoder = MediaCodec.createEncoderByType(VCODEC);} catch (IOException e) {Log.e(TAG, "create encoder failed.");e.printStackTrace();return;}ebi = new MediaCodec.BufferInfo();presentationTimeUs = new Date().getTime() * 1000;// start the encoder.// @see https://developer.android.com/reference/android/media/MediaCodec.htmlMediaFormat format = MediaFormat.createVideoFormat(MediaFormat.MIMETYPE_VIDEO_AVC, vsize.width, vsize.height);format.setInteger(MediaFormat.KEY_BIT_RATE, 125000);format.setInteger(MediaFormat.KEY_FRAME_RATE, 15);format.setInteger(MediaFormat.KEY_COLOR_FORMAT, chooseColorFormat());format.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 5);encoder.configure(format, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);encoder.start();Log.i(TAG, "encoder start");

其中，colorFormat需要从编码器支持的格式中选取，否则会有不支持的错误：

    // choose the right supported color format. @see below:// https://developer.android.com/reference/android/media/MediaCodecInfo.html// https://developer.android.com/reference/android/media/MediaCodecInfo.CodecCapabilities.htmlprivate int chooseColorFormat() {MediaCodecInfo ci = null;int nbCodecs = MediaCodecList.getCodecCount();for (int i = 0; i < nbCodecs; i++) {MediaCodecInfo mci = MediaCodecList.getCodecInfoAt(i);if (!mci.isEncoder()) {continue;}String[] types = mci.getSupportedTypes();for (int j = 0; j < types.length; j++) {if (types[j].equalsIgnoreCase(VCODEC)) {//Log.i(TAG, String.format("encoder %s types: %s", mci.getName(), types[j]));ci = mci;break;}}}int matchedColorFormat = 0;MediaCodecInfo.CodecCapabilities cc = ci.getCapabilitiesForType(VCODEC);for (int i = 0; i < cc.colorFormats.length; i++) {int cf = cc.colorFormats[i];//Log.i(TAG, String.format("encoder %s supports color fomart %d", ci.getName(), cf));// choose YUV for h.264, prefer the bigger one.if (cf >= cc.COLOR_FormatYUV411Planar && cf <= cc.COLOR_FormatYUV422SemiPlanar) {if (cf > matchedColorFormat) {matchedColorFormat = cf;}}}Log.i(TAG, String.format("encoder %s choose color format %d", ci.getName(), matchedColorFormat));return matchedColorFormat;}

第三个环节，在YUV图像回调中，送给编码器，并获取输出：

        // when got YUV frame from camera.// @see https://developer.android.com/reference/android/media/MediaCodec.htmlfinal Camera.PreviewCallback onYuvFrame = new Camera.PreviewCallback() {@Overridepublic void onPreviewFrame(byte[] data, Camera camera) {//Log.i(TAG, String.format("got YUV image, size=%d", data.length));// feed the encoder with yuv frame, got the encoded 264 es stream.ByteBuffer[] inBuffers = encoder.getInputBuffers();ByteBuffer[] outBuffers = encoder.getOutputBuffers();if (true) {int inBufferIndex = encoder.dequeueInputBuffer(-1);//Log.i(TAG, String.format("try to dequeue input buffer, ii=%d", inBufferIndex));if (inBufferIndex >= 0) {ByteBuffer bb = inBuffers[inBufferIndex];bb.clear();bb.put(data, 0, data.length);long pts = new Date().getTime() * 1000 - presentationTimeUs;//Log.i(TAG, String.format("feed YUV to encode %dB, pts=%d", data.length, pts / 1000));encoder.queueInputBuffer(inBufferIndex, 0, data.length, pts, 0);}for (;;) {int outBufferIndex = encoder.dequeueOutputBuffer(ebi, 0);//Log.i(TAG, String.format("try to dequeue output buffer, ii=%d, oi=%d", inBufferIndex, outBufferIndex));if (outBufferIndex >= 0) {ByteBuffer bb = outBuffers[outBufferIndex];onEncodedAnnexbFrame(bb, ebi);encoder.releaseOutputBuffer(outBufferIndex, false);}if (outBufferIndex < 0) {break;}}}// to fetch next frame.
                camera.addCallbackBuffer(buffer);}};

MUX为FLV流

获取编码的annexb数据后，调用函数发送到服务器：

    // when got encoded h264 es stream.private void onEncodedAnnexbFrame(ByteBuffer es, MediaCodec.BufferInfo bi) {try {muxer.writeSampleData(videoTrack, es, bi);} catch (Exception e) {Log.e(TAG, "muxer write sample failed.");e.printStackTrace();}}

最后这个环节，一般会用librtmp或者srslibrtmp，或者ffmpeg发送。如果服务器能直接支持http post，那么就可以使用HttpURLConnection直接发送了。SRS3将会支持HTTP-FLV推流；因此只需要将编码的annexb格式的数据，转换成flv后发送给SRS服务器。

SRS2支持了HTTP FLV Stream caster，也就是支持POST一个flv流到服务器，就相当于RTMP的publish了。可以直接使用android-publisher提供的FlvMuxer，将annexb数据打包发送，参考：https://github.com/simple-rtmp-server/android-publisher

其中，annexb打包的过程如下：

        public void writeVideoSample(final ByteBuffer bb, MediaCodec.BufferInfo bi) throws Exception {int pts = (int)(bi.presentationTimeUs / 1000);int dts = (int)pts;ArrayList<SrsAnnexbFrame> ibps = new ArrayList<SrsAnnexbFrame>();int frame_type = SrsCodecVideoAVCFrame.InterFrame;//Log.i(TAG, String.format("video %d/%d bytes, offset=%d, position=%d, pts=%d", bb.remaining(), bi.size, bi.offset, bb.position(), pts));// send each frame.while (bb.position() < bi.size) {SrsAnnexbFrame frame = avc.annexb_demux(bb, bi);// 5bits, 7.3.1 NAL unit syntax,// H.264-AVC-ISO_IEC_14496-10.pdf, page 44.//  7: SPS, 8: PPS, 5: I Frame, 1: P Frameint nal_unit_type = (int)(frame.frame.get(0) & 0x1f);if (nal_unit_type == SrsAvcNaluType.SPS || nal_unit_type == SrsAvcNaluType.PPS) {Log.i(TAG, String.format("annexb demux %dB, pts=%d, frame=%dB, nalu=%d", bi.size, pts, frame.size, nal_unit_type));}// for IDR frame, the frame is keyframe.if (nal_unit_type == SrsAvcNaluType.IDR) {frame_type = SrsCodecVideoAVCFrame.KeyFrame;}// ignore the nalu type aud(9)if (nal_unit_type == SrsAvcNaluType.AccessUnitDelimiter) {continue;}// for spsif (avc.is_sps(frame)) {byte[] sps = new byte[frame.size];frame.frame.get(sps);if (utils.srs_bytes_equals(h264_sps, sps)) {continue;}h264_sps_changed = true;h264_sps = sps;continue;}// for ppsif (avc.is_pps(frame)) {byte[] pps = new byte[frame.size];frame.frame.get(pps);if (utils.srs_bytes_equals(h264_pps, pps)) {continue;}h264_pps_changed = true;h264_pps = pps;continue;}// ibp frame.SrsAnnexbFrame nalu_header = avc.mux_ibp_frame(frame);ibps.add(nalu_header);ibps.add(frame);}write_h264_sps_pps(dts, pts);write_h264_ipb_frame(ibps, frame_type, dts, pts);}

至于发送到服务器，其实就是使用系统的HTTP客户端。代码如下：

    private void reconnect() throws Exception {// when bos not null, already connected.if (bos != null) {return;}disconnect();URL u = new URL(url);conn = (HttpURLConnection)u.openConnection();Log.i(TAG, String.format("worker: connect to SRS by url=%s", url));conn.setDoOutput(true);conn.setChunkedStreamingMode(0);conn.setRequestProperty("Content-Type", "application/octet-stream");bos = new BufferedOutputStream(conn.getOutputStream());Log.i(TAG, String.format("worker: muxer opened, url=%s", url));// write 13B header// 9bytes header and 4bytes first previous-tag-sizebyte[] flv_header = new byte[]{'F', 'L', 'V', // Signatures "FLV"(byte) 0x01, // File version (for example, 0x01 for FLV version 1)(byte) 0x00, // 4, audio; 1, video; 5 audio+video.(byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x09, // DataOffset UI32 The length of this header in bytes(byte) 0x00, (byte) 0x00, (byte) 0x00, (byte) 0x00};bos.write(flv_header);bos.flush();Log.i(TAG, String.format("worker: flv header ok."));sendFlvTag(bos, videoSequenceHeader);}private void sendFlvTag(BufferedOutputStream bos, SrsFlvFrame frame) throws IOException {if (frame == null) {return;}if (frame.frame_type == SrsCodecVideoAVCFrame.KeyFrame) {Log.i(TAG, String.format("worker: got frame type=%d, dts=%d, size=%dB", frame.type, frame.dts, frame.tag.size));} else {//Log.i(TAG, String.format("worker: got frame type=%d, dts=%d, size=%dB", frame.type, frame.dts, frame.tag.size));
        }// cache the sequence header.if (frame.type == SrsCodecFlvTag.Video && frame.avc_aac_type == SrsCodecVideoAVCType.SequenceHeader) {videoSequenceHeader = frame;}if (bos == null || frame.tag.size <= 0) {return;}// write the 11B flv tag headerByteBuffer th = ByteBuffer.allocate(11);// Reserved UB [2]// Filter UB [1]// TagType UB [5]// DataSize UI24int tag_size = (int)((frame.tag.size & 0x00FFFFFF) | ((frame.type & 0x1F) << 24));th.putInt(tag_size);// Timestamp UI24// TimestampExtended UI8int time = (int)((frame.dts << 8) & 0xFFFFFF00) | ((frame.dts >> 24) & 0x000000FF);th.putInt(time);// StreamID UI24 Always 0.th.put((byte)0);th.put((byte)0);th.put((byte)0);bos.write(th.array());// write the flv tag data.byte[] data = frame.tag.frame.array();bos.write(data, 0, frame.tag.size);// write the 4B previous tag size.// @remark, we append the tag size, this is different to SRS which write RTMP packet.ByteBuffer pps = ByteBuffer.allocate(4);pps.putInt((int)(frame.tag.size + 11));bos.write(pps.array());bos.flush();if (frame.frame_type == SrsCodecVideoAVCFrame.KeyFrame) {Log.i(TAG, String.format("worker: send frame type=%d, dts=%d, size=%dB, tag_size=%#x, time=%#x",frame.type, frame.dts, frame.tag.size, tag_size, time));}}

全部使用Java代码，最后apk编译出来才1405KB，稳定性也高很多，我已经在上班路上直播过了，除了码率低不太清楚，还没有死掉过。

转载于:https://www.cnblogs.com/zhujiabin/p/6812877.html