From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from perceval.ideasonboard.com ([95.142.166.194]:33759 "EHLO perceval.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751356Ab2HANPl (ORCPT ); Wed, 1 Aug 2012 09:15:41 -0400 From: Laurent Pinchart To: Bhupesh SHARMA Cc: "linux-usb@vger.kernel.org" , "linux-media@vger.kernel.org" Subject: Re: Query regarding the support and testing of MJPEG frame type in the UVC webcam gadget Date: Wed, 01 Aug 2012 15:15:47 +0200 Message-ID: <3577370.FUYPT1zGjj@avalon> In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-media-owner@vger.kernel.org List-ID: Hi Bhupesh, On Wednesday 01 August 2012 14:26:33 Bhupesh SHARMA wrote: > Hi Laurent, > > I have a query for you regarding the support and testing of MJPEG frame type > in the UVC webcam gadget. > > I see that in the webcam.c gadget, the 720p and VGA MJPEG uvc formats are > supported. I was trying the same out and got confused because the data > arriving from a real video capture video supporting JPEG will have no fixed > size. We will have the JPEG defined Start-of-Frame and End-of-Frame markers > defining the boundary of the JPEG frame. > > But for almost all JPEG video capture devices even if we have kept a frame > size of VGA initially, the final frame size will be a compressed version > (with the compression depending on the nature of the scene, so a flat scene > will have high compression and hence less frame size) of VGA and will not > be equal to 640 * 480. > > So I couldn't exactly get why the dwMaxVideoFrameBufferSize is kept as > 614400 in webcam.c (see [1]). The dwMaxVideoFrameBufferSize value must be larger than or equal to the largest MJPEG frame size. As I have no idea what that value is, I've kept the same size as for uncompressed frames, which should be big enough (and most probably too big). > Can you please let me know your opinions and how you tested the UVC gadget's > MJPEG frame format. > > [1] http://lxr.linux.no/linux+v3.5/drivers/usb/gadget/webcam.c#L232 -- Regards, Laurent Pinchart