Hi,
I think it is not related with V4L2.
I read your code just now, I am not clear your code: picture2 =
avcodec_alloc_frame();
I have a program, which use V4L2 get camera data YUYV, and then sws_scale
it to YUV420P.
But the input & output data buffer are both allocated myself, not ffmpeg.
I grab them here, there are some self-defined type by typedef, but not hard
to understand, FYI.
// init something and buffer
rb_uint32 oyuv_size =ow*oh*2;
rb_uint32 conv_size = ow * oh * 1.5;
int srclines[4];
srclines[0] = ow * 2;
srclines[1] = 0;
srclines[2] = 0;
srclines[3] = 0;
rb_uint8 *mid_buf, *conv_buf[3];
mid_buf = (rb_uint8*) osdep_malloc(oyuv_size); // yuyv buffer
conv_buf[0] = (rb_uint8*) osdep_malloc(ow * oh); // yuv420p buffer
conv_buf[1] = (rb_uint8*) osdep_malloc(ow * oh / 2);
conv_buf[2] = (rb_uint8*) osdep_malloc(ow * oh / 2);
// ***** THEN******, SOME CODES to read v4l2 buffer data into mid_buf.
// last , sws_scale
int destlines[4];
destlines[0] = mDstW;
destlines[1] = mDstW / 2;
destlines[2] = mDstW / 2;
destlines[3] = 0;
img_convert_ctx2 = sws_getCachedContext((struct SwsContext*)
img_convert_ctx2, ow, oh,
PIX_FMT_YUYV422, mDstW, mDstH, PIX_FMT_YUV420P, 1, NULL, NULL,
NULL);
if (img_convert_ctx2 == NULL)
{
fprintf(stderr, "Cannot initialize the conversion context\n");
}
sws_scale((struct SwsContext*) img_convert_ctx2, mid_buf, srclines, 0,
mSrcH, conv_buf, destlines);
On Fri, Nov 12, 2010 at 11:35 AM, George Smart <[email protected]>wrote:
> 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><
> 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><
> 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
> _______________________________________________
> libav-user mailing list
> [email protected]
> https://lists.mplayerhq.hu/mailman/listinfo/libav-user
>
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