[英]ffmpeg produces bad output when called from execve in c++
我正在編寫一個涉及從c ++程序調用ffmpeg的c ++程序。 幾天前,我使用std :: system使其正常工作
std::system("ffmpeg -threads auto -y -r 1.74659 -i /mnt/ev_ramdsk/1/%05d-capture.jpg -px_fmt yuv420p -preset ultrafast -r 10 /mnt/ev_ramdsk/1/video.mp4");
但這現在只能工作一次,它會產生8MB左右的.mp4視頻,因此無法在任何地方播放。.因此,由於上一個問題的建議,我移至execve。
這是我的代碼
child_pid = fork();
if(child_pid < 0){
syslog(LOG_ERR, "ERROR: ffmpeg forking failed");
return false;
}
else if(child_pid > 0){
syslog(LOG_DEBUG, "DEBUG: forking succeeded, pid: %d", child_pid);
}
else if(child_pid == 0){
char *newargv[16];
for(int i=0; i < 15; i++) newargv[i] = (char *)malloc(sizeof(char) * 60); //allocate the array in memory
strcpy(newargv[0], "/usr/bin/ffmpeg");
strcpy(newargv[1], "-threads");
strcpy(newargv[2], "auto");
strcpy(newargv[3], "-y");
strcpy(newargv[4], "-framerate");
tempSS << fps;
strcpy(newargv[5], tempSS.str().c_str());
tempSS.str(std::string());
strcpy(newargv[6], "-i");
strcpy(newargv[7], std::string(conf->dir_ram + dest + "%05d-capture.jpg").c_str());
strcpy(newargv[8], "-pix_fmt");
strcpy(newargv[9], "yuv420p");
strcpy(newargv[10], "-preset");
strcpy(newargv[11], "ultrafast");
strcpy(newargv[12], "-r");
strcpy(newargv[13], "25");
strcpy(newargv[14], std::string(conf->dir_ram + dest + "video.mp4").c_str());
newargv[15] = NULL;
for(int i=0; i < 15; i++){
tempSS << "newargv[" << i << "] = \"" << newargv[i] << "\", ";
}
syslog(LOG_DEBUG, "DEBUG:newargv: %s", tempSS.str().c_str());
tempSS.str(std::string());
char *newenviron[] = { NULL };
if(execve(newargv[0], newargv, newenviron) == -1){
syslog(LOG_ERR, "ERROR: execve returned -1");
exit(EXIT_SUCCESS);
}
}
wpid = wait(&status);
syslog(LOG_DEBUG, "DEBUG: ffmpeg child terminated, pid: %d, status: %d", wpid, status);
syslog的輸出是:
May 28 00:25:03 SERVER dt_ev_maker[10471]: DEBUG: forking succeeded, pid: 10658
May 28 00:25:03 SERVER dt_ev_maker[10658]: DEBUG:newargv:
newargv[0] = "/usr/bin/ffmpeg",
newargv[1] = "-threads",
newargv[2] = "auto",
newargv[3] = "-y",
newargv[4] = "-framerate",
newargv[5] = "1.45097",
newargv[6] = "-i",
newargv[7] = "/mnt/ev_ramdsk/1/%05d-capture.jpg",
newargv[8] = "-pix_fmt",
newargv[9] = "yuv420p",
newargv[10] = "-preset",
newargv[11] = "ultrafast",
newargv[12] = "-r",
newargv[13] = "25",
newargv[14] = "/mnt/ev_ramdsk/1/video.mp4",
May 28 00:25:03 SERVER dt_ev_maker[10471]: DEBUG: ffmpeg child terminated, pid: 10658, status: 256
在這種情況下,視頻大小約為90B,並且也已損壞。
注意:如果我從命令行運行相同的命令,則視頻可以正常播放。
我究竟做錯了什么?
提前致謝!
編輯
感謝ouroborus(上面提交的更改),我可以制作18MB的視頻,但是我不能播放它們。
似乎execve()
需要它的數組具有最后一個為NULL
元素。 將newargv
數組擴展1,並將最后一個元素設置為NULL
然后再將其傳遞到execve()
。
參考: 第一次使用execve
因此,最終起作用的代碼是:
pid_t wpid, child_pid;
int status;
int fd = open(std::string(conf->dir_ram + "ffmpeg.txt").c_str(), O_CREAT | O_WRONLY, 0777);
if(fd < 0){
syslog(LOG_ERR, "ERROR: open returned -1");
return false;
}
child_pid = fork();
if(child_pid < 0){
syslog(LOG_ERR, "ERROR: ffmpeg forking failed");
return false;
}
else if(child_pid > 0){
syslog(LOG_DEBUG, "DEBUG: forking succeeded, pid: %d", child_pid);
}
else if(child_pid == 0){
if( close(1) < 0 ){
syslog(LOG_ERR, "ERROR: close returned -1");
return false;
}
if( dup2(fd, 1) < 0 ){
syslog(LOG_ERR, "ERROR: dup2 returned -1");
return false;
}
char *newargv[18];
for(int i=0; i < 17; i++) newargv[i] = (char *)malloc(sizeof(char) * 60); //allocate the array in memory
strcpy(newargv[0], conf->ffmpeg_path.c_str());
strcpy(newargv[1], "-threads");
strcpy(newargv[2], "auto");
strcpy(newargv[3], "-y");
strcpy(newargv[4], "-r");
tempSS << fps;
strcpy(newargv[5], tempSS.str().c_str());
tempSS.str(std::string());
strcpy(newargv[6], "-i");
strcpy(newargv[7], std::string(conf->dir_ram + dest + "%05d-capture.jpg").c_str());
strcpy(newargv[8], "-pix_fmt");
strcpy(newargv[9], "yuv420p");
strcpy(newargv[10], "-c:v");
strcpy(newargv[11], "libx264");
strcpy(newargv[12], "-preset");
strcpy(newargv[13], "ultrafast");
strcpy(newargv[14], "-r");
strcpy(newargv[15], conf->ffmpeg_rate.c_str());
strcpy(newargv[16], std::string(conf->dir_ram + dest + "video.mp4").c_str());
newargv[17] = NULL;
char *newenviron[] = { NULL };
if(execve(newargv[0], newargv, newenviron) == -1){
syslog(LOG_ERR, "ERROR: execve returned -1");
exit(EXIT_SUCCESS);
}
}
wpid = wait(&status);
如果我評論整個open()和dup2()部分,則視頻會損壞。 我不知道為什么,但沒有它不起作用。
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