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 09BB540379 for ; Mon, 20 Dec 2021 15:24:00 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id 5E79468AF81; Mon, 20 Dec 2021 17:23:58 +0200 (EET) Received: from relay3-d.mail.gandi.net (relay3-d.mail.gandi.net [217.70.183.195]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id BBBC368AD92 for ; Mon, 20 Dec 2021 17:23:51 +0200 (EET) Received: from localhost (213-47-68-29.cable.dynamic.surfer.at [213.47.68.29]) (Authenticated sender: michael@niedermayer.cc) by relay3-d.mail.gandi.net (Postfix) with ESMTPSA id DDF2A60012 for ; Mon, 20 Dec 2021 15:23:50 +0000 (UTC) Date: Mon, 20 Dec 2021 16:23:49 +0100 From: Michael Niedermayer To: FFmpeg development discussions and patches Message-ID: <20211220152349.GS2829255@pb2> References: <678798058a84fb8a30dcfaa177431607@canta.com.ar> MIME-Version: 1.0 In-Reply-To: <678798058a84fb8a30dcfaa177431607@canta.com.ar> Subject: Re: [FFmpeg-devel] Politics 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: multipart/mixed; boundary="===============1214421804789321484==" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: --===============1214421804789321484== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="5XpzJ2VIAxwqV82M" Content-Disposition: inline --5XpzJ2VIAxwqV82M Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Dec 20, 2021 at 11:06:44AM -0300, Daniel Cantar=EDn wrote: >=20 > >=20 > > consider a subtitle track > > consider 2 video tracks for US 30000/1001 fps and EU 25 fps > >=20 > > the 6th frame in the US track is at 0.2002 sec, the 5th in the EU track > > at 0.2sec > >=20 > >=20 > > if these differ and you want a subtitle to either stop displaying after > > the > > earlier or begin displaying after the earlier reliably. Then you need a > > timebase that can represent points within each such close encounter of > > frame > > times. > >=20 >=20 > So, this isn't a subtitle problem if subtitle timings are correct. You > let 0.2002 in the subtitle, players will decide the frame. You want to > match the frame with the content, then you transcode the video properly. > Am I losing something? >=20 > Then again, we're of course not discussing players. One may say "that's > not ffmpeg responsability", yet players are 90% of the time the main > reason we have to do any extra work with ffmpeg. If we discuss real > life scenarios, we should be discussing players. >=20 > I also fail to see why would somebody want a "frame-perfect" sync > between two videos with different FPS. That's absurd: there's no such > thing as "frame-perfect" in such scenarios. What you would want is video > timings to be honored. That is: FPS conversion to be faithful to video > timings and content. I can imagine such precision dealing with frames > being blurred and having to do lots of fine tuning in order to be able > to perceive a single frame off in subtitles. That would be the real > problematic situation, not any .0002 rounding. >=20 > So, I see your example as a case of "what would the player do with that > 0.2002 rounding" (in which case, we all know there would be two > different subtitle files/streams with different precision for each > video if it's THAT important) instead of "we need to change the timebase > to something 4 decimals precise multiplier to both videos". >=20 > And even if this fails and a frame is interpreted incorrectly in the > player, good luck finding anyone saying anything about it: nobody cares > about a single frame when it's about subtitles. People watching > subtitles are simply not looking at that. This isn't speedrunning: it's > translating and transcribing. People wants to understand what's going on > in the screen, not debugging video frames. >=20 > So, I see no "serious subtitle problem" nor anything close to > "unnaceptable" here. >=20 > Let's remark, as softworkz say, this are all fantasy scenarios, and the > patchset doesn't show any real precision problem so far. If anyone is > willing to share input files to test such possible precision problems, > I'm willing to do the tests. No such files so far. I am not sure the direction from which you approuch this is going to increase the chances this patch has. All stream types in libavformat/codec are timebase based, that was done because its exact (for some definition of exact at least) I think you should argue why this is the best way forward not why its not too bad also in a few places where a fixed timebase is used ffmpeg uses AV_TIME_BASE_Q which is micro not milli seconds. That suddenly allows exactly addressing individual frames and audio samples. And it should be easy to change to from ms, its just a *1000 it would weaken the precission argument thx [...] --=20 Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB The day soldiers stop bringing you their problems is the day you have stopp= ed=20 leading them. They have either lost confidence that you can help or conclud= ed=20 you do not care. Either case is a failure of leadership. - Colin Powell --5XpzJ2VIAxwqV82M Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iF0EABEIAB0WIQSf8hKLFH72cwut8TNhHseHBAsPqwUCYcCgAQAKCRBhHseHBAsP q7W7AJ0dABTgGfzI3k7tpYtyq9DxQ13n4wCePpkWzni00pcNIvVIZ+ZX3JY36ME= =b9eG -----END PGP SIGNATURE----- --5XpzJ2VIAxwqV82M-- --===============1214421804789321484== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ 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". --===============1214421804789321484==--