用libvlc 抓取解码后的帧数据

Posted 2020-08-27 小阳明

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_player  
    libvlc_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 playing  
    libvlc_media_player_stop (mp);  

    // Free the media_player  
    libvlc_media_player_release (mp);  

    libvlc_release (inst);  

    return 0;  
}