From owner-freebsd-multimedia Sun Dec 21 20:00:59 1997 Return-Path: Received: (from root@localhost) by hub.freebsd.org (8.8.7/8.8.7) id UAA23338 for multimedia-outgoing; Sun, 21 Dec 1997 20:00:59 -0800 (PST) (envelope-from owner-freebsd-multimedia) Received: from whqvax.picker.com (whqvax.picker.com [144.54.1.1]) by hub.freebsd.org (8.8.7/8.8.7) with SMTP id UAA23333 for ; Sun, 21 Dec 1997 20:00:57 -0800 (PST) (envelope-from rhh@ct.picker.com) Received: from ct.picker.com by whqvax.picker.com with SMTP; Sun, 21 Dec 1997 23:00:15 -0500 (EST) Received: from elmer.ct.picker.com by ct.picker.com (4.1/SMI-4.1) id AA00306; Sun, 21 Dec 97 23:00:15 EST Received: by elmer.ct.picker.com (SMI-8.6/SMI-SVR4) id WAA09020; Sun, 21 Dec 1997 22:59:47 -0500 Message-Id: <19971221225947.08124@ct.picker.com> Date: Sun, 21 Dec 1997 22:59:47 -0500 From: Randall Hopper To: Amancio Hasty Cc: multimedia@freebsd.org Subject: MPEG audio/video sync & Re: These mtv video pauses are murder References: <19971221222047.08726@ct.picker.com> <199712220329.TAA00402@rah.star-gate.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.81 In-Reply-To: <199712220329.TAA00402@rah.star-gate.com>; from Amancio Hasty on Sun, Dec 21, 1997 at 07:29:13PM -0800 Sender: owner-freebsd-multimedia@freebsd.org X-Loop: FreeBSD.org Precedence: bulk Amancio Hasty: |Yes, I know about the mtv plus the sound driver issue . Will try again |this week to sort it out with Tristan. We left the issue that Tristan |was supposed to use a new ioctl provided by Hannu once that gets |iron out and it works on linux, I will be happy to implement the |new sound driver ioctl for freebsd. Ok, sounds like plan. |Got to admit that once fxtv supports YUV it is going to be totally |awesome -- we should try to load up mpeg movies --- for instance |I think that we need a FreeBSD mpeg theme --- Perhaps a Daemon watching |Fxtv 8) There's an idea! It's got some PR possibilities too. An eye catcher for sure, and would promote FreeBSD in the process. (Now we just got to find us someone with good cartooning skills :-) Say, something I've been meaning to ask you and the group. Is there something in the MPEG system stream format that you know of which allows you to "attach" (or suggest a relation) between a particular point in the video and the audio streams. Or is that implicit in the interleaving. What I'm a little concerned about is that for longer recordings, without these attachments, the strea audio will likely slip out of sync with the video during playback (due to a dropped frame or two per second [or more] in the original recording). Fxtv does try to buffer the video stream so that it's 30fps, regardless of how many frames it had to skip during capture, but if this process is off by, for example let's say, 1 frame per second, after 30 seconds the audio is going to be out of sync with the video by 1 second. It's accuracy is better than that, but I know it's not perfect. If this is possible to address, I'd like to look at it for the next batch of mods. Really, its kind of a nutty process that goes on now because of the tools that are available. First fxtv writes a RAW capture file that has the audio/video interleaved (so we know the audio/video relationship). Then we separate those out into separate audio and video streams (video padded up to 30fps) so mpeg_encode can be used to build an MPEG video stream, and mpeg_audio can be used to encode an MPEG audio stream. Finally those streams are merged together with mplex into a MPEG system stream, where we hope the video still "lines-up" with the audio. Randall