用libvlc 抓取解码后的帧数据

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 = ;

int IMG_HEIGHT = ;

char in_buffer[**];

char out_buffer[**];

FILE *local;

int frameNum = ;

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 ; /* 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,,,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=;

 /* 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, );

    libvlc_video_set_format(mp, "RGBA", IMG_WIDTH, IMG_HEIGHT,IMG_WIDTH*);

    // 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/);

    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 ;

}