From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp4-g21.free.fr ([212.27.42.4]:38244 "EHLO smtp4-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754236AbZBSMU1 (ORCPT ); Thu, 19 Feb 2009 07:20:27 -0500 Received: from smtp4-g21.free.fr (localhost [127.0.0.1]) by smtp4-g21.free.fr (Postfix) with ESMTP id BBB834C8195 for ; Thu, 19 Feb 2009 13:20:21 +0100 (CET) Received: from localhost (lns-bzn-33-82-252-42-42.adsl.proxad.net [82.252.42.42]) by smtp4-g21.free.fr (Postfix) with ESMTP id B568E4C802E for ; Thu, 19 Feb 2009 13:20:18 +0100 (CET) Date: Thu, 19 Feb 2009 13:17:45 +0100 From: Jean-Francois Moine To: Linux Media Subject: Questions about VIDIOC_G_JPEGCOMP / VIDIOC_S_JPEGCOMP Message-ID: <20090219131745.455df4da@free.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit Sender: linux-media-owner@vger.kernel.org List-ID: Hi, The VIDIOC_G_JPEGCOMP / VIDIOC_S_JPEGCOMP v4l2 ioctls seem not to be used by many drivers / applications. They should! In some ms-win traces, there are automatic and dynamic adjustments of the JPEG quality according to... who knows? Also, most webcams do not include the quantization tables in the images. Then, (in gspca), these tables are added by the subdrivers with a quality defined by the testers and according to their taste. As I understand, the JPEGCOMP ioctls permit to set the JPEG quality and to define the content of the JPEG frames. If I implement these controls in gspca: - by default, I could not add the quantization and Huffman tables in the image frames, - the quality could be set dynamically, this value being used to load the quantization tables in the webcam and also to convert the images. The questions are: 1) May the driver refuse to set some values on VIDIOC_S_JPEGCOMP? For example, if it cannot add the Huffman table in the frames. 2) Will the VIDIOC_G_JPEGCOMP ioctl be used by the v4l library (for conversion purpose)? 3) Does anybody know a command line or X application which may get/set these JPEG parameters? Regards. -- Ken ar c'hentań | ** Breizh ha Linux atav! ** Jef | http://moinejf.free.fr/