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 CA3B4434BA for ; Thu, 14 Jul 2022 08:18:17 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 6365068BA1B; Thu, 14 Jul 2022 11:18:16 +0300 (EEST) Received: from mout-p-202.mailbox.org (mout-p-202.mailbox.org [80.241.56.172]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id B8E5C68B53C for ; Thu, 14 Jul 2022 11:18:09 +0300 (EEST) Received: from smtp102.mailbox.org (smtp102.mailbox.org [10.196.197.102]) (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-202.mailbox.org (Postfix) with ESMTPS id 4Lk6nC451Jz9sQ8 for ; Thu, 14 Jul 2022 10:18:07 +0200 (CEST) Message-ID: Date: Thu, 14 Jul 2022 13:48:05 +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> <9d40d05b-a4e2-4742-eb05-78adb9bcf2a2@gyani.pro> <165778653167.15564.9570120529877659142@lain.khirnov.net> From: Gyan Doshi In-Reply-To: <165778653167.15564.9570120529877659142@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 01:45 pm, Anton Khirnov wrote: > Quoting Gyan Doshi (2022-07-14 09:47:17) >> >> 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. > No more objections to this patch, with this fallback dropped. Thanks. Since n5.1 hasn't been tagged just yet; will cherry-pick. 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".