[Libav-user] Encoding a screenshot into a video using FFMPEG

[phuzE]

Thanks for your help, I discovered that my output video plays fine, but
only in ffplay (in WMP/WMPClassic/VLC) it shows the gray distorted screen.
I have made some changes to my code since the last update so I'll post what
is working for me at the bottom of this. Can anyone think of a reason why
the video would work well in ffplay and nothing else? Is there a setting
that's causing this? I moved the screen capture code to another function,
but it's similar with error checking for the getDIBits calls, which is
where my earlier screenshot error was occurring, and also creating a
COLORREF* rather than an RGBQUAD*.

AVCodec* codec;
AVCodecContext* c = NULL;
uint8_t* outbuf;
int i, out_size, outbuf_size;

avcodec_register_all();

printf("Video encoding\n");

// Find the mpeg1 video encoder
codec = avcodec_find_encoder(CODEC_ID_H264);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
else printf("H264 codec found\n");

c = avcodec_alloc_context3(codec);

c->bit_rate = 400000;
c->width = 1920; // resolution must be a multiple of two
(1280x720),(1900x1080),(720x480)
c->height = 1200;
c->time_base.num = 1; // framerate numerator
c->time_base.den = 25; // framerate denominator
c->gop_size = 10; // emit one intra frame every ten frames
c->max_b_frames = 1; // maximum number of b-frames between non b-frames
//c->keyint_min = 1; // minimum GOP size
//c->i_quant_factor = (float)0.71; // qscale factor between P and I frames
//c->b_frame_strategy = 20;
//c->qcompress = (float)0.6;
//c->qmin = 20; // minimum quantizer
//c->qmax = 51; // maximum quantizer
//c->max_qdiff = 4; // maximum quantizer difference between frames
//c->refs = 4; // number of reference frames
//c->trellis = 1; // trellis RD Quantization
c->pix_fmt = PIX_FMT_YUV420P;
c->codec_id = CODEC_ID_H264;
//c->codec_type = AVMEDIA_TYPE_VIDEO;

// Open the encoder
if (avcodec_open2(c, codec,NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(1);
}
else printf("H264 codec opened\n");

outbuf_size = 100000 + c->width*c->height*(32>>3);//*(32>>3); // alloc
image and output buffer
outbuf = static_cast<uint8_t *>(malloc(outbuf_size));
printf("Setting buffer size to: %d\n",outbuf_size);

FILE* f = fopen("example.mpg","wb");
if(!f) printf("x - Cannot open video file for writing\n");
else printf("Opened video file for writing\n");

// encode 5 seconds of video
for(i=0;i<STREAM_FRAME_RATE*STREAM_DURATION;i++) {
fflush(stdout);

screenCap();


int nbytes = avpicture_get_size(PIX_FMT_YUV420P, c->width, c->height);
uint8_t* outbuffer = (uint8_t*)av_malloc(nbytes*sizeof(uint8_t));

AVFrame* inpic = avcodec_alloc_frame();
AVFrame* outpic = avcodec_alloc_frame();


outpic->pts = (int64_t)((float)i * (1000.0/((float)(c->time_base.den))) *
90);
avpicture_fill((AVPicture*)inpic, (uint8_t*)pPixels, PIX_FMT_RGB32,
c->width, c->height); // Fill picture with image

avpicture_fill((AVPicture*)outpic, outbuffer, PIX_FMT_YUV420P, c->width,
c->height);
av_image_alloc(outpic->data, outpic->linesize, c->width, c->height,
c->pix_fmt, 1);

inpic->data[0] += inpic->linesize[0]*(screenHeight-1); // Flipping frame
inpic->linesize[0] = -inpic->linesize[0]; // Flipping frame

struct SwsContext* fooContext = sws_getContext(screenWidth, screenHeight,
PIX_FMT_RGB32, c->width, c->height, PIX_FMT_YUV420P, SWS_FAST_BILINEAR,
NULL, NULL, NULL);

sws_scale(fooContext, inpic->data, inpic->linesize, 0, c->height,
outpic->data, outpic->linesize);

// encode the image
out_size = avcodec_encode_video(c, outbuf, outbuf_size, outpic);
printf("Encoding frame %3d (size=%5d)\n", i, out_size);
fwrite(outbuf, 1, out_size, f);
delete [] pPixels;
av_free(outbuffer);
av_free(inpic);
av_free(outpic);
}

// get the delayed frames
for(; out_size; i++) {
fflush(stdout);

out_size = avcodec_encode_video(c, outbuf, outbuf_size, NULL);
printf("Writing frame %3d (size=%5d)\n", i, out_size);
fwrite(outbuf, 1, out_size, f);
}

// add sequence end code to have a real mpeg file
outbuf[0] = 0x00;
outbuf[1] = 0x00;
outbuf[2] = 0x01;
outbuf[3] = 0xb7;
fwrite(outbuf, 1, 4, f);
fclose(f);

avcodec_close(c);
free(outbuf);
av_free(c);
printf("Closed codec and Freed\n");



On Wed, Apr 17, 2013 at 3:50 AM, Steffen Ebersbach-2 [via libav-users] <
ml-node+s943685n4657296h60 at n4.nabble.com> wrote:

> Hi
>
>
> this is my code for making a video from a screenshot. I do not use the
> hbitmap directly, but rather a gdi element. But i think this is not
> necessary i do this or other reasons.  One Idea, because in your last
> picture the shell window is shown but the visual studio window is
> missing, can be that the copy desktop / window function from windows
> can't capy elements from directx and so on , only nativ stuff. This is
> because in most remote control softwares, no video is transmitted.
> I hope the codes help you.
>
> Steffen
>
> --------------------------------------------------
> HWND window;
> // get hwnd from your window / desktop / ...
>
> srcDC = GetDC(window);
> tarDC = CreateCompatibleDC(srcDC);
> m_pal = (HPALETTE) GetCurrentObject(srcDC, OBJ_PAL); //colors
>
> HBITMAP obmp, hbmp = CreateCompatibleBitmap(srcDC, pwidth , pheight);
> obmp = (HBITMAP) SelectObject(tarDC, hbmp); //connect hbmp to DC
>
> res = SendMessage(window,WM_PRINT, (WPARAM)tarDC,(LPARAM) PRF_CLIENT  |
> ~PRF_ERASEBKGND); // Copy BMP
> tarbmp = Gdiplus::Bitmap::FromHBITMAP(hbmp,m_pal);
>
> SelectObject(tarDC,obmp);
> DeleteObject(hbmp);
>
>
> //Stream and encoder
> av_register_all();
> avcodec_init();
>
> AVFormatContext *focontext;
> AVStream *videostm;
> AVCodec *videocodec;
> AVCodecContext *videocontext;
> AVFrame *aktframe;
> uint8_t *framebuf1;
> SwsContext *imgconvctx;
>
> //container
> focontext = av_alloc_format_context();
>
> //videostream
> videostm = av_new_stream(focontext,0);
> // define your parameters here
>
> videocodec = avcodec_find_encoder(CODEC_ID_MPEG2VIDEO);
> avcodec_open(videocontext, videocodec);
>
> focontext->video_codec_id = videocontext->codec_id;
> av_set_parameters(focontext,0);
>
>
> //frame
> aktframe = avcodec_alloc_frame();
> picsize = avpicture_get_size(PIX_FMT_YUV420P, width, height);
> framebuf1 = (uint8_t*) av_malloc(picsize);
> avpicture_fill( (AVPicture*)aktframe, framebuf1, PIX_FMT_YUV420P, width,
> height);
>
> imgconvctx = sws_getContext(width, height ,PIX_FMT_BGR24 ,width,
> height,PIX_FMT_YUV420P, SWS_BICUBIC , 0,0,0);
>
> //convert bmp
> uint8_t *inbuffer;
> Gdiplus::BitmapData inbmpdata;
> Gdiplus::Rect cltrct(0,0,width,height);
>
> newbmp->LockBits(&cltrct, Gdiplus::ImageLockModeRead
> ,PixelFormat24bppRGB , &inbmpdata);
>
> inbuffer = (uint8_t*) inbmpdata.Scan0;
> AVFrame *inframe = 0;
>
> inframe = avcodec_alloc_frame();
> avpicture_fill( (AVPicture*)inframe, inbuffer, PIX_FMT_BGR24, width,
> height);
> sws_scale(imgconvctx,inframe->data , inframe->linesize,0, height,
> aktframe->data , aktframe->linesize);
> int videobuf_size = videocontext->bit_rate *2;
>
> //open output
> url_fopen(&focontext->pb,"file.mpg" , URL_WRONLY)
> av_write_header(focontext);
>
> //encode and write frame
> av_init_packet(&avpkt);
> encsize = avcodec_encode_video(videocontext, videobuf ,videobuf_size,
> aktframe);
> avpkt.stream_index= videostm->index;
> avpkt.data= videobuf;
> avpkt.size= encsize;
>
> av_write_frame(focontext, &avpkt);
>
> // next frames
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