From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S267387AbUH1SEH (ORCPT ); Sat, 28 Aug 2004 14:04:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S267483AbUH1SEH (ORCPT ); Sat, 28 Aug 2004 14:04:07 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:4776 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S267387AbUH1SEE (ORCPT ); Sat, 28 Aug 2004 14:04:04 -0400 Subject: Re: reverse engineering pwcx From: Lee Revell To: Joel Jaeggli Cc: Albert Cahalan , linux-kernel mailing list , clemtaylor@comcast.net, qg@biodome.org, rogers@isi.edu In-Reply-To: References: <1093709838.434.6797.camel@cube> <1093710358.8611.22.camel@krustophenia.net> Content-Type: text/plain Message-Id: <1093716249.8611.45.camel@krustophenia.net> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Sat, 28 Aug 2004 14:04:10 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2004-08-28 at 13:53, Joel Jaeggli wrote: > On Sat, 28 Aug 2004, Lee Revell wrote: > > > > How do you account for the Slashdot poster's assertion that it's > > physically impossible to cram 640 x 480 worth of data down a USB 1.1 > > pipe? > > 640x480 = 307200 pixels > x 24 bits = 7372800 bits per frame (.9MB) > x 30 fps = 221184000 > > so that's 221mb/s for uncompressed 640x480. dv with 16bit pcm is 25Mb/s > typically which is still a bit more than double what you can reasonably > push through a usb1.1 port. raw you can push about 1.6 fp/s at 640x480 > through usb so your compression ratio needs to be order of 15 to 1 make > it fit reasonably with room for overhead. 15 to 1 is impossible without lossy compression. I am not really a video expert, but I know that it's impossible to losslessly compress audio more than 50-75%. Therefore there is no way it's 'True 640 x 480' as Philips' marketing claims. Unless you take 'true' to mean 'interpolated by the driver so your userspace program doesn't have to do it'. This is a stretch. Lee