Android平台GB28181设计开发的时候，有个功能必不可少的：实时快照，特别是用于执法记录仪等场景下，用于图像留底或分析等考量。

实时快照的实现并不难，目前实现有两种方式，一种是拿到数据（比如摄像头数据）后，直接上层编码，存取快照；另一种模式是，数据投递到JNI层，底层针对投递过来的编码前数据，做png编码，并保存到设定的目录下，今天我们主要探讨第二种实现模式。

我们在publisher实例初始化的时候，设置是否启用快照：

private void InitAndSetConfig() {int audio_opt = 1;int fps = 18;int gop = fps * 2;Log.i(TAG, "InitAndSetConfig video_width: " + video_width_ + " cur_video_height" + video_height_ + " imageRotationDegree:" + cameraImageRotationDegree_);publisherHandle = libPublisher.SmartPublisherOpen(context_, audio_opt, 3,  video_width_, video_height_);if (publisherHandle == 0) {Log.e(TAG, "sdk open failed!");return;}Log.i(TAG, "publisherHandle=" + publisherHandle);if(videoEncodeType == 1)  {int h264HWKbps = setHardwareEncoderKbps(true, video_width_, video_height_);h264HWKbps = h264HWKbps*fps/25;Log.i(TAG, "h264HWKbps: " + h264HWKbps);int isSupportH264HWEncoder = libPublisher.SetSmartPublisherVideoHWEncoder(publisherHandle, h264HWKbps);if (isSupportH264HWEncoder == 0) {libPublisher.SetNativeMediaNDK(publisherHandle, 1);Log.i(TAG, "Great, it supports h.264 hardware encoder!");}}else if (videoEncodeType == 2) {int hevcHWKbps = setHardwareEncoderKbps(false, video_width_, video_height_);hevcHWKbps = hevcHWKbps*fps/25;Log.i(TAG, "hevcHWKbps: " + hevcHWKbps);int isSupportHevcHWEncoder = libPublisher.SetSmartPublisherVideoHevcHWEncoder(publisherHandle, hevcHWKbps);if (isSupportHevcHWEncoder == 0) {libPublisher.SetNativeMediaNDK(publisherHandle, 1);Log.i(TAG, "Great, it supports hevc hardware encoder!");}}boolean is_sw_vbr_mode = true;if(is_sw_vbr_mode)	//H.264 software encoder{int is_enable_vbr = 1;int video_quality = CalVideoQuality(video_width_, video_height_, true);int vbr_max_bitrate = CalVbrMaxKBitRate(video_width_, video_height_);libPublisher.SmartPublisherSetSwVBRMode(publisherHandle, is_enable_vbr, video_quality, vbr_max_bitrate);}if (is_pcma_) {libPublisher.SmartPublisherSetAudioCodecType(publisherHandle, 3);} else {libPublisher.SmartPublisherSetAudioCodecType(publisherHandle, 1);}libPublisher.SetSmartPublisherEventCallbackV2(publisherHandle, new EventHandePublisherV2());libPublisher.SmartPublisherSetSWVideoEncoderProfile(publisherHandle, 3);libPublisher.SmartPublisherSetSWVideoEncoderSpeed(publisherHandle, 2);libPublisher.SmartPublisherSetGopInterval(publisherHandle, gop);libPublisher.SmartPublisherSetFPS(publisherHandle, fps);// libPublisher.SmartPublisherSetSWVideoBitRate(publisherHandle, 600, 1200);boolean is_noise_suppression = true;libPublisher.SmartPublisherSetNoiseSuppression(publisherHandle, is_noise_suppression ? 1 : 0);boolean is_agc = false;libPublisher.SmartPublisherSetAGC(publisherHandle, is_agc ? 1 : 0);int echo_cancel_delay = 0;libPublisher.SmartPublisherSetEchoCancellation(publisherHandle, 1, echo_cancel_delay);libPublisher.SmartPublisherSaveImageFlag(publisherHandle, 1);
}

记得留意最后一句：libPublisher.SmartPublisherSaveImageFlag(publisherHandle, 1);

相关接口说明如下：

 /*** Set if needs to save image during publishing stream(设置是否启用快照)** @param is_save_image: if with 1, it will save current image via the interface of SmartPlayerSaveImage(), if with 0: does not it** @return {0} if successful*/public native int SmartPublisherSaveImageFlag(long handle,  int is_save_image);

设置后，页面有需要实时快照的数据时，点击“实时快照”按钮即可，需要注意的是，实时快照需要存储路径和保存下来的快照文件名称。具体实现如下：

class ButtonCaptureImageListener implements View.OnClickListener {@SuppressLint("SimpleDateFormat")public void onClick(View v) {if(isPushingRtmp || isRecording || isRTSPPublisherRunning || isGB28181StreamRunning){String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date());String imageFileName = "dn_" + timeStamp;    //创建以时间命名的文件名称String imagePath = imageSavePath + "/" + imageFileName + ".png";Log.i(TAG, "imagePath:" + imagePath);libPublisher.SmartPublisherSaveCurImage(publisherHandle, imagePath);}else{Log.e(TAG, "快照失败，请确保在推送、录像、GB28181推送或内置RTSP服务发布状态..");}}
}

快照截取成功后，publisher实例会回调以下事件：

case NTSmartEventID.EVENT_DANIULIVE_ERC_PUBLISHER_CAPTURE_IMAGE:publisher_event = "快照: " + param1 + " 路径：" + param3;if (param1 == 0) {publisher_event = publisher_event + "截取快照成功..";} else {publisher_event = publisher_event + "截取快照失败..";}break;

由于实时快照，功能复杂度不高，而且也可以在上层实现，很容易被忽略，如果做的精细的话，还是需要开发者花费一定的心思。