From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ffbox0-bg.mplayerhq.hu (ffbox0-bg.ffmpeg.org [79.124.17.100]) by master.gitmailbox.com (Postfix) with ESMTP id 5C51D434A8 for ; Thu, 14 Jul 2022 06:46:29 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 0119468B9B4; Thu, 14 Jul 2022 09:46:26 +0300 (EEST) Received: from mail0.khirnov.net (red.khirnov.net [176.97.15.12]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 5380468B874 for ; Thu, 14 Jul 2022 09:46:21 +0300 (EEST) Received: from localhost (localhost [IPv6:::1]) by mail0.khirnov.net (Postfix) with ESMTP id 0BBB6240179 for ; Thu, 14 Jul 2022 08:46:21 +0200 (CEST) Received: from mail0.khirnov.net ([IPv6:::1]) by localhost (mail0.khirnov.net [IPv6:::1]) (amavisd-new, port 10024) with ESMTP id 8ERC28erXiBx for ; Thu, 14 Jul 2022 08:46:20 +0200 (CEST) Received: from lain.khirnov.net (lain.khirnov.net [IPv6:2001:67c:1138:4306::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256 client-signature RSA-PSS (2048 bits) client-digest SHA256) (Client CN "lain.khirnov.net", Issuer "smtp.khirnov.net SMTP CA" (verified OK)) by mail0.khirnov.net (Postfix) with ESMTPS id 2C34B2400F5 for ; Thu, 14 Jul 2022 08:46:20 +0200 (CEST) Received: by lain.khirnov.net (Postfix, from userid 1000) id 1FF581601B2; Thu, 14 Jul 2022 08:46:20 +0200 (CEST) From: Anton Khirnov To: FFmpeg development discussions and patches In-Reply-To: <1e188a5a-122d-fbf6-b888-b6dfe81b9f94@gyani.pro> References: <20220704162912.5577-1-ffmpeg@gyani.pro> <165718689777.31466.279724099132649515@lain.khirnov.net> <165747338953.25016.5154122227679155982@lain.khirnov.net> <1e188a5a-122d-fbf6-b888-b6dfe81b9f94@gyani.pro> Mail-Followup-To: FFmpeg development discussions and patches Date: Thu, 14 Jul 2022 08:46:20 +0200 Message-ID: <165778118010.15564.11436275642541493245@lain.khirnov.net> User-Agent: alot/0.8.1 MIME-Version: 1.0 Subject: Re: [FFmpeg-devel] [PATCH v3] ffmpeg: add option -isync X-BeenThere: ffmpeg-devel@ffmpeg.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: FFmpeg development discussions and patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: FFmpeg development discussions and patches Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: Quoting Gyan Doshi (2022-07-10 20:02:38) > > > On 2022-07-10 10:46 pm, Anton Khirnov wrote: > > Quoting Gyan Doshi (2022-07-08 05:56:21) > >> > >> On 2022-07-07 03:11 pm, Anton Khirnov wrote: > >>> Quoting Gyan Doshi (2022-07-04 18:29:12) > >>>> This is a per-file input option that adjusts an input's timestamps > >>>> with reference to another input, so that emitted packet timestamps > >>>> account for the difference between the start times of the two inputs. > >>>> > >>>> Typical use case is to sync two or more live inputs such as from capture > >>>> devices. Both the target and reference input source timestamps should be > >>>> based on the same clock source. > >>>> > >>>> If not all inputs have timestamps, the wallclock times at the time of > >>>> reception of inputs shall be used. FFmpeg must have been compiled with > >>>> thread support for this last case. > >>> I'm wondering if simply using the other input's InputFile.ts_offset > >>> wouldn't achieve the same effect with much less complexity. > >> That's what I initially did. But since the code can also use two other > >> sources for start times (start_time_realtime, first_pkt_wallclock), > >> those intervals may not exactly match the difference between > >> fmctx->start_times so I use a generic calculation. > > In what cases is it better to use either of those two other sources? > > > > As per the commit message, the timestamps of both inputs are supposed to > > come from the same clock. Then it seems to me that offsetting each of > > those streams by different amounts would break synchronization rather > > than improve it. > > The first preference, when available, stores the epoch time closest to > time of capture. That would eliminate some jitter. > The 2nd preference is the fmctx->start_time. The 3rd is the reception > wallclock. It is a fallback. It will likely lead to the worst sync. In which cases is this fallback useful? I would expect that all transports you'd want to use this with will have working timestamps. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-request@ffmpeg.org with subject "unsubscribe".