基于OpenCV的视频图像组态 (13)：VLC Player解码帧数据

网上示例

vlc是一套优秀的开源媒体库，其特点是提供了完整的流媒体框架， 用它可以非常方便的实现抓取解码帧的功能。

与此功能有关的关键API为

libvlc_video_set_callbacks /*设置回调，用来抓取解码后的帧*/

libvlc_video_set_format /*设置解码帧的格式 yuv or rgba ?*/

这个函数将三个函数指针作为参数

/*callback function, lock the shared memory, and tell vlc

where to put the output frame data*/

static void *lock(void *data, void **p_pixels);

 

 

/*##get the out frame data AND u can save it to file, or sent it

to a next module*/

static void unlock(void *data, void *id, void *const *p_pixels);

 

/*how to display the result frame data, u can let vlc do not pop out the displaying gui via this fuction. */

static void display(void *data, void *id);

 

下面是完整示例子：

#include "stdafx.h"#include <Windows.h>#include "vlc/vlc.h"#include <vector>#include <qmutex>#include <sstream>#include <qimage> QMutex g_mutex;bool g_isInit = false;int IMG_WIDTH = 640;int IMG_HEIGHT = 480;char in_buffer[640*480*4];char out_buffer[640*480*4];FILE *local;int frameNum = 0; const char* TestFile = "b040_20170106.dat";//////////////////////////////////////////////////////////////////////////static void *lock(void *data, void **p_pixels){g_mutex.lock();*p_pixels = out_buffer; /*tell VLC to put decoded data to this buffer*/return 0; /* picture identifier, not needed here */} /*##get the argb picture AND save to file*/static void unlock(void *data, void *id, void *const *p_pixels){QImage image((unsigned char*)out_buffer,640,480,QImage::Format_ARGB32);std::ostringstream oss;oss << "d:/img"<< frameNum<< ".jpg";frameNum++;image.save(oss.str().c_str());g_mutex.unlock();} static void display(void *data, void *id){/* do not display the video */(void) data;}   //////////////////////////////////////////////////////////////////////////int main(int argc, char* argv[]){libvlc_instance_t * inst;libvlc_media_player_t *mp;libvlc_media_t *m; libvlc_time_t length;int wait_time=5000; /* Load the VLC engine */inst = libvlc_new (int(options.size()), options.data());  // Configure any transcoding or streaming// options for the media source.options.clear(); //Create a new item//Method 1://m = libvlc_media_new_location (inst, "file:///F:\\movie\\cuc_ieschool.flv");//Screen Capture//m = libvlc_media_new_location (inst, "screen://");//Method 2:m = libvlc_media_new_path (inst, "D:\\warehouse\\data\\615\\haze.mp4");/* Create a media player playing environment */mp = libvlc_media_player_new_from_media (m);  /* No need to keep the media now */libvlc_media_release (m); /*##comment the followint 2 lines , if you want the out frame display in screen*/libvlc_video_set_callbacks(mp, lock, unlock, display, 0);libvlc_video_set_format(mp, "RGBA", IMG_WIDTH, IMG_HEIGHT,IMG_WIDTH*4); // play the media_playerlibvlc_media_player_play (mp); //wait until the tracks are created_sleep (wait_time);length = libvlc_media_player_get_length(mp);IMG_WIDTH = libvlc_video_get_width(mp);IMG_HEIGHT = libvlc_video_get_height(mp);printf("Stream Duration: %ds\n",length/1000);printf("Resolution: %d x %d\n",IMG_WIDTH,IMG_HEIGHT); //Let it play_sleep (length-wait_time); // Stop playinglibvlc_media_player_stop (mp); // Free the media_playerlibvlc_media_player_release (mp); libvlc_release (inst); return 0;}



改编实现
 
仔细研究网上代码，最终将VLCWrapper改造一下。
static void *lock(void *opaque, void **plane) {    VLCWrapper *vlcWrapper = (VLCWrapper*)opaque;    vlcWrapper->Lock();    *plane = vlcWrapper->FMat.data;    return NULL;} static void unlock(void *opaque, void *pic, void * const *plane) {    VLCWrapper *vlcWrapper = (VLCWrapper*)opaque;    vlcWrapper->Draw();    vlcWrapper->Unlock();} static void display(void *opaque, void *pic) {    (void)opaque;} void __fastcall VLCWrapper::Lock() {    EnterCriticalSection(&g_VlcCriticalSection);} void __fastcall VLCWrapper::Unlock() {    LeaveCriticalSection(&g_VlcCriticalSection);}void __fastcall VLCWrapper::Draw() {    static int radius = 100; // 测试画一个不断长大的圆    radius += 3;    if(radius > 1000)        radius = 100;    circle(FMat, cv::Point(100, 100), radius / 10, cv::Scalar(255, 255, 255), 3);    GlobalOpenCVObject->DrawMat(hWnd, FMat, FDisplayWidth, FDisplayHeight);} void __fastcall VLCWrapper::SetTriggleCallback(bool value) {Lock();try {FTriggleCallback = value;if(FTriggleCallback)libvlc_video_set_callbacks(pImpl_->pMediaPlayer_, lock, unlock, display, this);elselibvlc_video_set_callbacks(pImpl_->pMediaPlayer_, NULL, NULL, NULL, NULL);} __finally {Unlock();}}


演示效果
  
 (因为视频文件大小限制，所以最终生成的帧频为2，导致看起来很不流畅)