I am currently writing an application that read frames from camera, modify them, and save them into a video file. I'm planing to do it with ffmpeg. There's rarely a documentation about ffmpeg. I can't find a way. Does any know how to do it?
I need it to be done on unix, and in C or C++. Does any can provide some instructions?
Thanks.
EDIT:
Sorry, I haven't write clearly. I want some developer APIs to write frames to a video file. I open up camera stream, I get every single frame, then I save them into a video file with those APIs available in ffmpeg's public apis. So using command line tool actually doesn't help me. And I've seen output_example.c under the ffmpeg src folder. It's pretty great that I may copy some parts of the code directly without change. And I am still looking for a easier way.
Also, I'm thinking of porting my app to iPhone, as far as I know, only ffmpeg has been ported on iPhone. GStreamer is based on glib, and it's all GNU stuff. I'm not sure if I can get it work on iPhone. So ffmpeg is still the best choice for now.
Any comments is appreciated.
This might help get you started - the documentation is available, but newer features tend to be documented in ffmpeg's man pages.
The frames need to be numbered sequentially.
ffmpeg -f image2 -framerate 25 -i frame_%d.jpg -c:v libx264 -crf 22 video.mp4
-f defines the format-framerate defines the frame rate-i defines the input file/s ... %d specifies numbered files .. add 0's
to specify padding, e.g. %05d for zero-padded five-digit numbers.-vcodec selects the video codec-crf specifies a rate control method, used to define how the x264 stream is
encodedvideo.mp4 is the output file
For more info, see the Slideshow guide.
If other solutions than ffmpeg are feasible for you, you might want to look at GStreamer. I think it might be just the right thing for your case, and there's quite some documentation out there.
You can do what you require without using a library, as in unix you can pipe RGBA data into a program, so you can do:
In your program:
char myimage[640*480*4];
// read data into myimage
fputs(myimage,1,640*480*4,stdout);
And in a script that runs your program:
./myprogram | \
mencoder /dev/stdin -demuxer rawvideo -rawvideo w=640:h=480:fps=30:format=rgba \
-ovc lavc -lavcopts vcodec=mpeg4:vbitrate=9000000 \
-oac copy -o output.avi
I believe you can also use ffmpeg this way, or x264. You can also start the encoder from within your program, and write to a pipe (making the whole process as simple if you were using a library).
While not quite what you want, and not suitable for iPhone development, it does have the advantage that Unix will automatically use a second processor for the encoding.
