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 B1F2D42439 for ; Sat, 18 Dec 2021 13:36:22 +0000 (UTC) Received: from [127.0.1.1] (localhost [127.0.0.1]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTP id AB90768AE7F; Sat, 18 Dec 2021 15:36:20 +0200 (EET) Received: from relay4-d.mail.gandi.net (relay4-d.mail.gandi.net [217.70.183.196]) by ffbox0-bg.mplayerhq.hu (Postfix) with ESMTPS id 5BCFF68AD15 for ; Sat, 18 Dec 2021 15:36:14 +0200 (EET) Received: from localhost (213-47-68-29.cable.dynamic.surfer.at [213.47.68.29]) (Authenticated sender: michael@niedermayer.cc) by relay4-d.mail.gandi.net (Postfix) with ESMTPSA id 7D3B5E0005 for ; Sat, 18 Dec 2021 13:36:13 +0000 (UTC) Date: Sat, 18 Dec 2021 14:36:12 +0100 From: Michael Niedermayer To: FFmpeg development discussions and patches Message-ID: <20211218133612.GL2829255@pb2> References: <20211216132151.8216-1-jamrial@gmail.com> <92861361-f316-78a5-3c72-1e279d2a9f8c@passwd.hu> <20211217112417.GG2829255@pb2> <5d14188-a4b0-4978-104c-59595fed8137@passwd.hu> MIME-Version: 1.0 In-Reply-To: <5d14188-a4b0-4978-104c-59595fed8137@passwd.hu> Subject: Re: [FFmpeg-devel] [PATCH 000/279 v2] New channel layout API 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="===============7648158509502558591==" Errors-To: ffmpeg-devel-bounces@ffmpeg.org Sender: "ffmpeg-devel" Archived-At: List-Archive: List-Post: --===============7648158509502558591== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="zr6TmWAmZ5MJ4JPk" Content-Disposition: inline --zr6TmWAmZ5MJ4JPk Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Dec 17, 2021 at 07:04:08PM +0100, Marton Balint wrote: >=20 >=20 > On Fri, 17 Dec 2021, Michael Niedermayer wrote: >=20 > > On Fri, Dec 17, 2021 at 01:04:19AM +0100, Marton Balint wrote: > > >=20 > > >=20 > > > On Thu, 16 Dec 2021, James Almer wrote: > > >=20 > > > > Resending the first two patches only, since this is meant to > > > > show the implementation of one of the several suggestions made > > > > in the previous set that need to be discussed and hopefully > > > > resolved in a call. > > >=20 > > > Can you push the full branch somewhere? > > >=20 > > > >=20 > > > > The proposals so far to extend the API to support either custom > > > > labels for channels are, or some form of extra user information. > > > >=20 > > > > - Fixed array of bytes to hold a label. Simple solution, but > > > > the labels will have a hard limit that can only be extended > > > > with a major bump. This is what i implemented in this version. > > > > - "char *name" per channel that the user may allocate and the > > > > API will manage, duplicate and free. Simple solution, and the > > > > name can be arbitrarily long, but inefficient (av_strdup() per > > > > channel with a custom label on layout copy). > > > > - "const char *name" per channel for compile time constants, or > > > > that the user may allocate and free. Very efficient, but for > > > > non compile time strings ensuring they outlive the layout can > > > > be tricky. > > > > - Refcounted AVChannelCustom with a dictionary. This can't be > > > > done with AVBufferRef, so it would require some other form > > > > of reference counting. And a dictionary may add quite a bit of > > > > complexity to the API, as you can set anything on them. > > >=20 > > > Until we have proper refcounting API we can make the AVBufferRef in > > > AVChannelLayout a void *, and only allow channel_layout functions to > > > dereference it as an AVBufferRef. This would mean adding some extra h= elper > > > functions to channel layout, but overall it is not unsolvable. > > >=20 > > > The real question is that if you want to use refcounting and add help= ers to > > > query / replace per-channel metadata, or you find the idea too heavy = weight > > > and would like to stick to flat structs. > >=20 > > what is the advantage of refcounting for channel metadata ? > > is it about the used memory, about the reduced need to copy ? >=20 > Basicly it is the ability to store per-channel metadata in avdictionary, > because otherwise it would have to be copyed, and avdictionary is very > ineffective at copying because of many mallocs. >=20 > >=20 > > what kind of metadata and what size do you expect ? > > bytes, kilobytes, megabytes, gigabytes per channel ? >=20 > Usually, nothing, because most format don't have support for per-channel > metadata. In some cases it is going to be a couple of textual metadata > key-value pairs, such as language, label, group, speaker, positon, so 4-5 > dynamically allocated string pairs, plus the AVDictionary itself, multipl= ied > by the number of channels in a layout. >=20 > >=20 > > what is the overhead for dynamic allocation and ref counting? > > that is at which point does it even make sense ? >=20 > I don't have exact measurements. It is generally felt that copying > AVDictionary per-channel is a huge overhead for something as lightweight = as > an audio frame which is a 2-4 kB per channel at most and only a couple of > allocs usually not dependant on the number of channels. That's why > refcounting was proposed. I was thinking more at a AVStream / AVCodecParameters level. How will a demuxer transport such metadata over a AVPacket into a decoder outputting metadata-filled AVFrames? thx [...] --=20 Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Let us carefully observe those good qualities wherein our enemies excel us and endeavor to excel them, by avoiding what is faulty, and imitating what is excellent in them. -- Plutarch --zr6TmWAmZ5MJ4JPk Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iF0EABEIAB0WIQSf8hKLFH72cwut8TNhHseHBAsPqwUCYb3jyAAKCRBhHseHBAsP qxp3AJ9ZHhcOZpivK+V8dgpepCbqmzFbzwCfbs/8+xpuF6CYSGtxcqD1O0RW8aA= =rU8b -----END PGP SIGNATURE----- --zr6TmWAmZ5MJ4JPk-- --===============7648158509502558591== 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". --===============7648158509502558591==--