[MPlayer-dev-eng] MJPEG camera support for v4l2 driver

[Trent Piepho]

On Sat, 26 May 2007, Vladimir Voroshilov wrote:
> 2007/5/25, Trent Piepho <xyzzy at speakeasy.org>:
> > > The patch should be "fixed" now and updated to match with the current SVN-version.
> >
> >      int h = priv->format.fmt.pix.height;
> >      int d = pixfmt2depth(priv->format.fmt.pix.pixelformat);
> >      int bytesperline = w*d/8;
> > +    int sizeimage = priv->format.fmt.pix.sizeimage ? priv->format.fmt.pix.sizeimage : (bytesperline * h);
> >
> > The existing code to calculate the image size shouldn't even be necessary.
> > sizeimage is suppose to already contain it.
> priv->format.fmt.pix.sizeimage will always have nonzero value. Thus
> sizeimage variable will be always equal to
> priv->format.fmt.pix.sizeimage. Did i undestand right?

Yes, sizeimage should never be zero, or it's a bug in the driver.

> > For the copy frame function, it's not quite right either.  sizeimage in the
> > pixel format is the maximum size of a frame.  jpeg compressed frames will
> > not all be the same size and some will be smaller.  The "bytesused" field
> > in the v4l2_buffer returned by DQBUF should contain the actual frame size.
> This will require another ringbuffer to store "bytesused" values for
> each frame for future return in get_video_frame_size.

Wouldn't it be simpler to just have one ring buffer of v4l2_buffer structs?