我想记录我的电脑屏幕（在我的Windows机器上使用gdigrab）并将保存的视频文件存储在我的磁盘上作为mp4或mpg文件。我找到了一个示例代码来抓取屏幕并显示它在SDL窗口中：http://xwk.iteye.com/blog/2125720（代码位于页面底部并有英文版本），ffmpeg多路复用示例https://ffmpeg.org/doxygen/trunk/muxing_8c-source.html似乎能够帮助将音频和视频编码为所需的输出视频文件。
我试图将这两者结合起来，使用格式上下文来抓取屏幕（AVFormatContext * pFormatCtx;在我的代码中）和单独的格式上下文来编写所需的视频文件（AVFormatContext * outFormatContextEncoded;）。从输入流中读取数据包（屏幕抓取流）我直接将写入数据包编码到输出文件中，如我的代码所示。我保留了SDL代码，这样我就可以看到我正在录制的内容。我的代码是我修改后的write_video_frame（ ）功能。
代码构建正常，但vlc无法播放输出视频。当我运行命令
时ffmpeg -i filename.mpg
我得到了这个输出
[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
我在这里做错了吗？我是ffmpeg的新手，对此有任何指导都非常感谢。谢谢你的时间。
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;
}
答案 0 :(得分：0)
原来我遇到了这里讨论的问题：使用avcodec_encode_video2函数Segmentation fault while avcodec_encode_video2。
修改后的完整代码如下。它可以录制并保存到磁盘但它有一些问题。录制的视频有点扭曲，不清楚，我仍在调查可能的原因。我也扯掉了SDL部分因为我不再需要它了。对此非常欢迎！
代码：
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;
}