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 6F392434B1 for ; Thu, 14 Jul 2022 07:47:33 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 9449F68B9B9; Thu, 14 Jul 2022 10:47:30 +0300 (EEST) Received: from mout-p-101.mailbox.org (mout-p-101.mailbox.org [80.241.56.151]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 76A3768B65F for ; Thu, 14 Jul 2022 10:47:22 +0300 (EEST) Received: from smtp1.mailbox.org (smtp1.mailbox.org [10.196.197.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-384) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-101.mailbox.org (Postfix) with ESMTPS id 4Lk65h0SGCz9sWZ for ; Thu, 14 Jul 2022 09:47:20 +0200 (CEST) Message-ID: <9d40d05b-a4e2-4742-eb05-78adb9bcf2a2@gyani.pro> Date: Thu, 14 Jul 2022 13:17:17 +0530 MIME-Version: 1.0 Content-Language: en-US To: ffmpeg-devel@ffmpeg.org 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> <165778118010.15564.11436275642541493245@lain.khirnov.net> From: Gyan Doshi In-Reply-To: <165778118010.15564.11436275642541493245@lain.khirnov.net> 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-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: On 2022-07-14 12:16 pm, Anton Khirnov wrote: > 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. Agreed. I just kept it as a last resort scenario. Can do without it. Regards, Gyan _______________________________________________ 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".