ffmpeg录制屏幕并将视频文件另存为.mpg到磁盘

Question

I want to record the screen of my pc (using gdigrab on my windows machine) and store the saved video file on my disk as an mp4 or mpg file .I have found an example piece of code that grabs the screen and shows it in an SDL window here : http://xwk.iteye.com/blog/2125720 (The code is on the bottom of the page and has an english version) and the ffmpeg muxing example https://ffmpeg.org/doxygen/trunk/muxing_8c-source.html seems to be able to help encode audio and video into a desired output video file.

I have tried to combine these two by having a format context for grabbing the screen (AVFormatContext *pFormatCtx; in my code ) and a separate format context to write the desired video file (AVFormatContext *outFormatContextEncoded;).Within the loop to read packets from the input stream( screen grab stream) I directly encode write packets to the output file as shown in my code.I have kept the SDL code so I can see what I am recording.Below is my code with my modified write_video_frame() function .

The code builds OK but the output video can't be played by vlc. When I run the command

ffmpeg -i filename.mpg

I get this output

[mpeg @ 003fed20] probed stream 0 failed
[mpeg @ 003fed20] Stream #0: not enough frames to estimate rate; consider increasing probesize
[mpeg @ 003fed20] Could not find codec parameters for stream 0 (Video: none): unknown codec
Consider increasing the value for the 'analyzeduration' and 'probesize' options
karamage.mpg: could not find codec parameters
Input #0, mpeg, from 'karamage.mpg':
  Duration: 19:30:09.25, start: 37545.438756, bitrate: 2 kb/s
    Stream #0:0[0x1e0]: Video: none, 90k tbr, 90k tbn
At least one output file must be specified

Am I doing something wrong here? I am new to ffmpeg and any guidance on this is highly appreciated.Thank you for your time.

int main(int argc, char* argv[])
{

    AVFormatContext *pFormatCtx;

    int             i, videoindex;
    AVCodecContext  *pCodecCtx;
    AVCodec         *pCodec;

    av_register_all();
    avformat_network_init();

    //Localy defined structure.
    OutputStream outVideoStream = { 0 };

    const char *filename;
    AVOutputFormat *outFormatEncoded;
    AVFormatContext *outFormatContextEncoded;
    AVCodec *videoCodec;

    filename="karamage.mpg";

    int ret1;

    int have_video = 0, have_audio = 0;
    int encode_video = 0, encode_audio = 0;


    AVDictionary *opt = NULL;



    //ASSIGN STH TO THE FORMAT CONTEXT.
    pFormatCtx = avformat_alloc_context();

    //
    //Use this when opening a local file.
    //char filepath[]="src01_480x272_22.h265";
    //avformat_open_input(&pFormatCtx,filepath,NULL,NULL)

    //Register Device
    avdevice_register_all();

    //Use gdigrab
    AVDictionary* options = NULL;
    //Set some options
    //grabbing frame rate
    //av_dict_set(&options,"framerate","5",0);
    //The distance from the left edge of the screen or desktop
    //av_dict_set(&options,"offset_x","20",0);
    //The distance from the top edge of the screen or desktop
    //av_dict_set(&options,"offset_y","40",0);
    //Video frame size. The default is to capture the full screen
    //av_dict_set(&options,"video_size","640x480",0);
    AVInputFormat *ifmt=av_find_input_format("gdigrab");
    if(avformat_open_input(&pFormatCtx,"desktop",ifmt,&options)!=0){
        printf("Couldn't open input stream.\n");
        return -1;
    }

    if(avformat_find_stream_info(pFormatCtx,NULL)<0)
    {
        printf("Couldn't find stream information.\n");
        return -1;
    }
    videoindex=-1;
    for(i=0; i<pFormatCtx->nb_streams; i++) 
        if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO)
        {
            videoindex=i;
            break;
        }
    if(videoindex==-1)
    {
        printf("Didn't find a video stream.\n");
        return -1;
    }
    pCodecCtx=pFormatCtx->streams[videoindex]->codec;
    pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
    if(pCodec==NULL)
    {
        printf("Codec not found.\n");
        return -1;
    }
    if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
    {
        printf("Could not open codec.\n");
        return -1;
    }


    AVFrame *pFrame,*pFrameYUV;
    pFrame=avcodec_alloc_frame();
    pFrameYUV=avcodec_alloc_frame();

    //PIX_FMT_YUV420P WHAT DOES THIS SAY ABOUT THE FORMAT??
    uint8_t *out_buffer=(uint8_t *)av_malloc(avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));


    avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);

    //<<<<<<<<<<<-------PREP WORK TO WRITE ENCODED VIDEO FILES-----

    avformat_alloc_output_context2(&outFormatContextEncoded, NULL, NULL, filename);
    if (!outFormatContextEncoded) {
        printf("Could not deduce output format from file extension: using MPEG.\n");
        avformat_alloc_output_context2(&outFormatContextEncoded, NULL, "mpeg", filename);
    }
    if (!outFormatContextEncoded)
        return 1;

    outFormatEncoded=outFormatContextEncoded->oformat;


     //THIS CREATES THE STREAMS(AUDIO AND VIDEO) ADDED TO OUR OUTPUT STREAM

    if (outFormatEncoded->video_codec != AV_CODEC_ID_NONE) {

        //YOUR VIDEO AND AUDIO PROPS ARE SET HERE.
        add_stream(&outVideoStream, outFormatContextEncoded, &videoCodec, outFormatEncoded->video_codec);
        have_video = 1;
        encode_video = 1;
    }


     // Now that all the parameters are set, we can open the audio and
     // video codecs and allocate the necessary encode buffers. 
    if (have_video)
        open_video(outFormatContextEncoded, videoCodec, &outVideoStream, opt);

     av_dump_format(outFormatContextEncoded, 0, filename, 1);


      /* open the output file, if needed */
    if (!(outFormatEncoded->flags & AVFMT_NOFILE)) {
        ret1 = avio_open(&outFormatContextEncoded->pb, filename, AVIO_FLAG_WRITE);
        if (ret1 < 0) {
            //fprintf(stderr, "Could not open '%s': %s\n", filename,
            //        av_err2str(ret));
            fprintf(stderr, "Could not open your dumb file.\n");
            return 1;
        }
    }


    /* Write the stream header, if any. */
    ret1 = avformat_write_header(outFormatContextEncoded, &opt);
    if (ret1 < 0) {
        //fprintf(stderr, "Error occurred when opening output file: %s\n",
         //       av_err2str(ret));
        fprintf(stderr, "Error occurred when opening output file\n");
        return 1;
    }


    //<<<<<<<<<<<-------PREP WORK TO WRITE ENCODED VIDEO FILES-----

    //SDL----------------------------
    if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {  
        printf( "Could not initialize SDL - %s\n", SDL_GetError()); 
        return -1;
    } 
    int screen_w=640,screen_h=360;
    const SDL_VideoInfo *vi = SDL_GetVideoInfo();
    //Half of the Desktop's width and height.
    screen_w = vi->current_w/2;
    screen_h = vi->current_h/2;
    SDL_Surface *screen; 
    screen = SDL_SetVideoMode(screen_w, screen_h, 0,0);

    if(!screen) {  
        printf("SDL: could not set video mode - exiting:%s\n",SDL_GetError());  
        return -1;
    }
    SDL_Overlay *bmp; 
    bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,SDL_YV12_OVERLAY, screen); 
    SDL_Rect rect;
    //SDL End------------------------
    int ret, got_picture;

    AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));

    //TRY TO INIT THE PACKET HERE
     av_init_packet(packet);


    //Output Information-----------------------------
    printf("File Information---------------------\n");
    av_dump_format(pFormatCtx,0,NULL,0);
    printf("-------------------------------------------------\n");

    struct SwsContext *img_convert_ctx;
    img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); 
    //------------------------------
    //
    while(av_read_frame(pFormatCtx, packet)>=0)
    {

        if(packet->stream_index==videoindex)
        {
            //HERE WE DECODE THE PACKET INTO THE FRAME
            ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);
            if(ret < 0)
            {
                printf("Decode Error.\n");
                return -1;
            }
            if(got_picture)
            {

                //THIS IS WHERE WE DO STH WITH THE FRAME WE JUST GOT FROM THE STREAM
                //FREE AREA--START
                //IN HERE YOU CAN WORK WITH THE FRAME OF THE PACKET.
                write_video_frame(outFormatContextEncoded, &outVideoStream,packet);


                //FREE AREA--END
                sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);


                SDL_LockYUVOverlay(bmp);
                bmp->pixels[0]=pFrameYUV->data[0];
                bmp->pixels[2]=pFrameYUV->data[1];
                bmp->pixels[1]=pFrameYUV->data[2];     
                bmp->pitches[0]=pFrameYUV->linesize[0];
                bmp->pitches[2]=pFrameYUV->linesize[1];   
                bmp->pitches[1]=pFrameYUV->linesize[2];
                SDL_UnlockYUVOverlay(bmp); 
                rect.x = 0;    
                rect.y = 0;    
                rect.w = screen_w;    
                rect.h = screen_h;  
                SDL_DisplayYUVOverlay(bmp, &rect); 
                //Delay 40ms----WHY THIS DELAY????
                SDL_Delay(40);
            }
        }
        av_free_packet(packet);
    }//THE LOOP TO PULL PACKETS FROM THE FORMAT CONTEXT ENDS HERE.

    //AFTER THE WHILE LOOP WE DO SOME CLEANING

    //av_read_pause(context);


     av_write_trailer(outFormatContextEncoded);
     close_stream(outFormatContextEncoded, &outVideoStream);
     if (!(outFormatContextEncoded->flags & AVFMT_NOFILE))
        /* Close the output file. */
        avio_close(outFormatContextEncoded->pb);

    /* free the stream */
    avformat_free_context(outFormatContextEncoded);



    //STOP DOING YOUR CLEANING
    sws_freeContext(img_convert_ctx);



    SDL_Quit();

    av_free(out_buffer);
    av_free(pFrameYUV);
    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}



/*
 * encode one video frame and send it to the muxer
 * return 1 when encoding is finished, 0 otherwise
 */
static int write_video_frame(AVFormatContext *oc, OutputStream *ost,AVPacket * pkt11)
{
    int ret;
    AVCodecContext *c;
    AVFrame *frame;
    int got_packet = 0;

    c = ost->st->codec;

    //DO NOT NEED THIS FRAME.
    //frame = get_video_frame(ost);

    if (oc->oformat->flags & AVFMT_RAWPICTURE) {

        //IGNORE THIS FOR A MOMENT
        /* a hack to avoid data copy with some raw video muxers */
        AVPacket pkt;
        av_init_packet(&pkt);

        if (!frame)
            return 1;

        pkt.flags        |= AV_PKT_FLAG_KEY;
        pkt.stream_index  = ost->st->index;
        pkt.data          = (uint8_t *)frame;
        pkt.size          = sizeof(AVPicture);

        pkt.pts = pkt.dts = frame->pts;
        av_packet_rescale_ts(&pkt, c->time_base, ost->st->time_base);

        ret = av_interleaved_write_frame(oc, &pkt);
    } else {

            ret = write_frame(oc, &c->time_base, ost->st, pkt11);

    }

    if (ret < 0) {
        fprintf(stderr, "Error while writing video frame: %s\n");
        exit(1);
    }


    return 1;
}

Answer 1

Turns out I was having the issue discussed here : Segmentation fault while avcodec_encode_video2 with the avcodec_encode_video2 function.

The revised full code is below.It can record and save to the disk but it has some problems.The recorded video is kind of distorted and it is not clear and I am still investigating the possible reason.Also I ripped off the SDL part as I do not need it anymore.Any improvement on this is highly welcome!

The code:

extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavdevice/avdevice.h"


#include <libavutil/opt.h>
#include <libavutil/channel_layout.h>
#include <libavutil/common.h>
#include <libavutil/imgutils.h>
#include <libavutil/mathematics.h>
#include <libavutil/samplefmt.h>
//SDL
#include "SDL.h"
#include "SDL_thread.h"
}

//Output YUV420P
#define OUTPUT_YUV420P 0
//'1' Use Dshow
//'0' Use GDIgrab
#define USE_DSHOW 0

int main(int argc, char* argv[])
{

    //1.WE HAVE THE FORMAT CONTEXT
    //THIS IS FROM THE DESKTOP GRAB STREAM.
    AVFormatContext *pFormatCtx;
    int             i, videoindex;
    AVCodecContext  *pCodecCtx;
    AVCodec         *pCodec;

    av_register_all();
    avformat_network_init();

    //ASSIGN STH TO THE FORMAT CONTEXT.
    pFormatCtx = avformat_alloc_context();

    //Register Device
    avdevice_register_all();
    //Windows
#ifdef _WIN32
#if USE_DSHOW
    //Use dshow
    //
    //Need to Install screen-capture-recorder
    //screen-capture-recorder
    //Website: http://sourceforge.net/projects/screencapturer/
    //
    AVInputFormat *ifmt=av_find_input_format("dshow");
    //if(avformat_open_input(&pFormatCtx,"video=screen-capture-recorder",ifmt,NULL)!=0){
    if(avformat_open_input(&pFormatCtx,"video=UScreenCapture",ifmt,NULL)!=0){
        printf("Couldn't open input stream.\n");
        return -1;
    }
#else
    //Use gdigrab
    AVDictionary* options = NULL;
    //Set some options
    //grabbing frame rate
    //av_dict_set(&options,"framerate","5",0);
    //The distance from the left edge of the screen or desktop
    //av_dict_set(&options,"offset_x","20",0);
    //The distance from the top edge of the screen or desktop
    //av_dict_set(&options,"offset_y","40",0);
    //Video frame size. The default is to capture the full screen
    //av_dict_set(&options,"video_size","640x480",0);
    AVInputFormat *ifmt=av_find_input_format("gdigrab");
    if(avformat_open_input(&pFormatCtx,"desktop",ifmt,&options)!=0){
        printf("Couldn't open input stream.\n");
        return -1;
    }

#endif
#endif//FOR THE WIN32 THING.

    if(avformat_find_stream_info(pFormatCtx,NULL)<0)
    {
        printf("Couldn't find stream information.\n");
        return -1;
    }
    videoindex=-1;
    for(i=0; i<pFormatCtx->nb_streams; i++)
        if(pFormatCtx->streams[i]->codec->codec_type
                ==AVMEDIA_TYPE_VIDEO)
        {
            videoindex=i;
            break;
        }
    if(videoindex==-1)
    {
        printf("Didn't find a video stream.\n");
        return -1;
    }
    pCodecCtx=pFormatCtx->streams[videoindex]->codec;
    pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
    if(pCodec==NULL)
    {
        printf("Codec not found.\n");
        return -1;
    }
    if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
    {
        printf("Could not open codec.\n");
        return -1;
    }

    //THIS IS WHERE YOU CONTROL THE FORMAT(THROUGH FRAMES).
    AVFrame *pFrame;//,*pFrameYUV;

    pFrame=av_frame_alloc();

    int ret, got_picture;

    AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));

    //TRY TO INIT THE PACKET HERE
     av_init_packet(packet);


    //Output Information-----------------------------
    printf("File Information---------------------\n");
    av_dump_format(pFormatCtx,0,NULL,0);
    printf("-------------------------------------------------\n");


//<<--FOR WRITING MPG FILES
    //<<--START:PREPARE TO WRITE YOUR MPG FILE.

    const char * filename="test.mpg";
    int codec_id=   AV_CODEC_ID_MPEG1VIDEO;


    AVCodec *codec11;
    AVCodecContext *outContext= NULL;
    int got_output;
    FILE *f;
    AVPacket pkt;
    uint8_t endcode[] = { 0, 0, 1, 0xb7 };

    printf("Encode video file %s\n", filename);

    /* find the mpeg1 video encoder */
    codec11 = avcodec_find_encoder((AVCodecID)codec_id);
    if (!codec11) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }

    outContext = avcodec_alloc_context3(codec11);
    if (!outContext) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    /* put sample parameters */
    outContext->bit_rate = 400000;
    /* resolution must be a multiple of two */
    outContext->width = 352;
    outContext->height = 288;


    /* frames per second */
    outContext->time_base.num=1;
    outContext->time_base.den=25;

    /* emit one intra frame every ten frames
     * check frame pict_type before passing frame
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
     * then gop_size is ignored and the output of encoder
     * will always be I frame irrespective to gop_size
     */
    outContext->gop_size = 10;
    outContext->max_b_frames = 1;
    outContext->pix_fmt = AV_PIX_FMT_YUV420P;

    if (codec_id == AV_CODEC_ID_H264)
        av_opt_set(outContext->priv_data, "preset", "slow", 0);

    /* open it */
    if (avcodec_open2(outContext, codec11, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }

    f = fopen(filename, "wb");
    if (!f) {
        fprintf(stderr, "Could not open %s\n", filename);
        exit(1);
    }


    AVFrame *outframe = av_frame_alloc();
    int nbytes = avpicture_get_size(outContext->pix_fmt,
                                   outContext->width,
                                   outContext->height);

    uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes);

   //ASSOCIATE THE FRAME TO THE ALLOCATED BUFFER.
    avpicture_fill((AVPicture*)outframe, outbuffer,
                   AV_PIX_FMT_YUV420P,
                   outContext->width, outContext->height);

    SwsContext* swsCtx_ ;
    swsCtx_= sws_getContext(pCodecCtx->width,
                            pCodecCtx->height,
                            pCodecCtx->pix_fmt,
                            outContext->width, outContext->height,
                            outContext->pix_fmt,
                            SWS_BICUBIC, NULL, NULL, NULL);


    //HERE WE START PULLING PACKETS FROM THE SPECIFIED FORMAT CONTEXT.
    while(av_read_frame(pFormatCtx, packet)>=0)
    {
        if(packet->stream_index==videoindex)
        {
            ret= avcodec_decode_video2(pCodecCtx,
                                         pFrame,
                                         &got_picture,packet );
            if(ret < 0)
            {
                printf("Decode Error.\n");
                return -1;
            }
            if(got_picture)
            {

            sws_scale(swsCtx_, pFrame->data, pFrame->linesize,
                  0, pCodecCtx->height, outframe->data,
                  outframe->linesize);


            av_init_packet(&pkt);
            pkt.data = NULL;    // packet data will be allocated by the encoder
            pkt.size = 0;


            ret = avcodec_encode_video2(outContext, &pkt, outframe, &got_output);
            if (ret < 0) {
               fprintf(stderr, "Error encoding frame\n");
               exit(1);
              }

            if (got_output) {
                printf("Write frame %3d (size=%5d)\n", i, pkt.size);
                fwrite(pkt.data, 1, pkt.size, f);
                av_free_packet(&pkt);
               }

            }
        }

        av_free_packet(packet);
    }//THE LOOP TO PULL PACKETS FROM THE FORMAT CONTEXT ENDS HERE.

    /* add sequence end code to have a real mpeg file */
    fwrite(endcode, 1, sizeof(endcode), f);
    fclose(f);

    avcodec_close(outContext);
    av_free(outContext);
    //av_freep(&frame->data[0]);
    //av_frame_free(&frame);

    //THIS WAS ADDED LATER
    av_free(outbuffer);

    avcodec_close(pCodecCtx);
    avformat_close_input(&pFormatCtx);

    return 0;
}