How to grab ffmpeg's output as binary and write it to a file on the fly such that video players-CodePudding

The

The file is always ~2kB regardless of how long I run the program: "No data" is shown repeatedly in the console output.

Why doesn't it work? If it is not just a bug, how can I grab the stream as binary at some point, and write it at the end to a file that VLC can read?

Update

New code after applying Craig Estey's fix to my stupid mistake. The end result is that the MPEG-TS frames don't seem to shift anymore but the file writing stops partway into one of the first few frames (the console only shows a few ">" symbols and then stays silent, c.f. code).

#include <stdio.h> #include <stdlib.h> #include <conio.h> #define BUFSIZE 188 // MPEG-TS packet size int main() { char *cmd = (char *) "ffmpeg -i \"rtsp://127.0.0.1:8554/test.sdp\" -c:v copy -c:a copy -f mpegts pipe:1 -loglevel quiet"; char buf[BUFSIZE]; FILE *ptr, *file; file = fopen("./out.ts", "w"); if (!file) { printf("Failed to open output file for writing, aborting"); abort(); } if ((ptr = popen(cmd, "r")) != NULL) { printf("Writing RTSP stream to file..."); while(!kbhit()) { ssize_t rlen = fread(&buf, sizeof(char), BUFSIZE, ptr); if(rlen != 0) { printf(">"); fwrite(buf, sizeof(char), rlen, file); fflush(file); } } pclose(ptr); } else { printf("Failed to open pipe from ffmpeg command, aborting"); } printf("End of program"); fclose(file); return 0; }

This can be tested on any computer with VLC and a webcam: open VLC, open capture device, capture mode directshow, (switch "play" for "stream"), next, display locally, select RTSP, Add, path=/test.sdp, next, transcoding=H264 MP3 (TS), replace rtsp://:8554/ with rtsp://127.0.0.1:8554/ in the generated command line, stream.

To test that streaming is ok, you can just open a command terminal and enter "ffmpeg -i "rtsp://127.0.0.1:8554/test.sdp" -c:v copy -c:a copy -f mpegts pipe:1 -loglevel quiet", the terminal should fill up with binary data.

To test the program, just compile, run, and open out.ts after the program has run.

CodePudding user response：

This may not be your total problem, but you're ignoring the return value from fread.

Pipe reads can return a short length. But, you're always writing BUFSIZE on output.

Here's the refactored code (I nop'ed the winX code because I'm on linux):

#include <stdio.h> #include <stdlib.h> //#include <conio.h> #define BUFSIZE 188 // MPEG-TS packet size int main() { char *cmd = (char *) "ffmpeg -i \"rtsp://admin:[email protected]:554/h264Preview_01_main\" -c:v copy -c:a copy -f mpegts pipe:1 -loglevel quiet"; char buf[BUFSIZE]; FILE *ptr, *file; file = fopen("./out.bin", "w"); if (!file) { printf("Failed to open output file for writing, aborting"); abort(); } if ((ptr = popen(cmd, "r")) != NULL) { printf("Writing RTSP stream to file..."); while (1) { #if 0 if (kbhit()) break; #endif // NOTE/BUG: this ignores the returned length and may write too much #if 0 if (fread(&buf, sizeof(char), BUFSIZE, ptr) != 0) { fwrite(buf, sizeof(char), BUFSIZE, file); } else { printf("No data\n"); } #else ssize_t rlen = fread(&buf, sizeof(char), BUFSIZE, ptr); if (rlen <= 0) break; fwrite(buf, sizeof(char), rlen, file); #endif } pclose(ptr); } else { printf("Failed to open pipe from ffmpeg command, aborting"); } printf("End of program"); fclose(file); return 0; }

In the code above, I've used cpp conditionals to denote old vs. new code:

#if 0 // old code #else // new code #endif #if 1 // new code #endif

Note: this can be cleaned up by running the file through unifdef -k

CodePudding user response：

Since #include <conio.h> is Windows only, we may conclude that you are using Windows.
(The rest of the code looks like Linux, so MinGW compiler is probably used...)

In Linux all files are binary files, but in Windows, the default file format is text file.
I guess that the execution ends on the first EOF character (the issue may also be related to "new line" characters).

We have to open the files as binary files:

Replace file = fopen("./out.bin", "w"); with:

file = fopen("./out.bin", "wb");

Replace ptr = popen(cmd, "r") with:

ptr = popen(cmd, "rb")

Corrected code:

#include <stdio.h> #include <stdlib.h> #include <conio.h> #define BUFSIZE 188 // MPEG-TS packet size int main() { const char *cmd = "ffmpeg -i \"rtsp://127.0.0.1:8554/test.sdp\" -c:v copy -c:a copy -f mpegts pipe:1 -loglevel quiet"; char buf[BUFSIZE]; FILE *ptr, *file; file = fopen("./out.ts", "wb"); //Open file as binary file if (!file) { printf("Failed to open output file for writing, aborting"); abort(); } if ((ptr = popen(cmd, "rb")) != NULL) { //Open pipe as binary file printf("Writing RTSP stream to file..."); while(!kbhit()) { ssize_t rlen = fread(&buf, sizeof(char), BUFSIZE, ptr); if(rlen != 0) { printf(">"); fwrite(buf, sizeof(char), rlen, file); fflush(file); } } pclose(ptr); } else { printf("Failed to open pipe from ffmpeg command, aborting"); } printf("End of program"); fclose(file); return 0; }