Dear libav-user
I wonder if anybody would be able to help me with encoding video from a
webcam with ffmpeg libraries. I have taken the video encoder example,
and modified it slightly to allow me to encode frames as they arrive
from the webcam. My source code for the ffmpeg part can be found here:
http://www.ee.ucl.ac.uk/~zceed42/ffmpeg.html
<http://www.ee.ucl.ac.uk/%7Ezceed42/ffmpeg.html> .
Frames are read from the webcam by V4L2. init_video_encode is called
with a filename, and sets up the codec, etc. close_video_encode is
called to close the video encoder, finish files, free memory, etc.
video_encode is called with a pointer to a frame of video from V4L2. It
is set as below, inside V4L2. These are the only options which work
with the webcams I have.
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
Inside my code, http://www.ee.ucl.ac.uk/~zceed42/ffmpeg.html
<http://www.ee.ucl.ac.uk/%7Ezceed42/ffmpeg.html>, I take data from the
V4L2 pointer, *p, with the av_fill command, and fill picture (AVFrame):
avpicture_fill( (AVPicture *) picture, p, PIX_FMT_YUYV422,
c->width, c->height);
The input video from V4L2 is YUYV422 (I believe - VLC tells me it's
YUY2, which Google tells me is the same thing). I am trying to use:
eSC = sws_getContext(c->width, c->height, PIX_FMT_YUYV422,
c->width, c->height, PIX_FMT_YUV420P, SWS_FAST_BILINEAR, NULL, NULL, NULL);
sws_scale(eSC, (const uint8_t* const*) picture->data,
picture->linesize, 0, c->height, picture2->data, picture2->linesize);
To convert from YUYV422 to YUV420P for
avcodec_encode_video(c, outbuf, outbuf_size, picture2);
Picture and Picture2 are AVFrames before and after the conversion,
respectively.
The problem is, the sws_scale() call SIGSEGV's (Segmentation Faults). I
have had a hunt about with gdb and can't find out the reason. I was
hoping someone with experience could point me in the right direction.
I've Googled a fair bit, and can't seem to get my head around this one...
I am also open to suggestions of replacing my V4L2 interface with
something more ffmpeg friendly - I read that ffmeg can get frames from
webcam directly??
Thanks in advance for your time.
George Smart, M1GEO
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