From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0033CC432C2 for ; Wed, 25 Sep 2019 09:51:00 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C963C214D9 for ; Wed, 25 Sep 2019 09:50:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C963C214D9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:47623 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iD3wo-0000YW-Sa for qemu-devel@archiver.kernel.org; Wed, 25 Sep 2019 05:50:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35668) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iD3vo-0007sP-Ae for qemu-devel@nongnu.org; Wed, 25 Sep 2019 05:49:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iD3vn-0007Il-4v for qemu-devel@nongnu.org; Wed, 25 Sep 2019 05:49:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38256) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iD3vm-0007HS-TH for qemu-devel@nongnu.org; Wed, 25 Sep 2019 05:49:55 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2A05EC057F31; Wed, 25 Sep 2019 09:49:54 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-117-142.ams2.redhat.com [10.36.117.142]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8C4FC608C0; Wed, 25 Sep 2019 09:49:51 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 2194C113864E; Wed, 25 Sep 2019 11:49:50 +0200 (CEST) From: Markus Armbruster To: =?utf-8?B?Wm9sdMOhbiBLxZF2w6Fnw7M=?= Subject: Re: [PATCH v4 15/24] audio: add mixing-engine option (documentation) References: <68c4b4bd438e9cb5c97aed32ee31e3dabd96cbf6.1568927990.git.DirtY.iCE.hu@gmail.com> <87sgonma7v.fsf@dusky.pond.sub.org> <4d24c95c-0e98-2646-0b1a-6c7b3afe0e90@gmail.com> Date: Wed, 25 Sep 2019 11:49:50 +0200 In-Reply-To: <4d24c95c-0e98-2646-0b1a-6c7b3afe0e90@gmail.com> (=?utf-8?B?IlpvbHTDoW4JS8WRdsOhZ8OzIidz?= message of "Tue, 24 Sep 2019 02:21:32 +0200") Message-ID: <87wodwyabl.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Wed, 25 Sep 2019 09:49:54 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" "Zolt=C3=A1n K=C5=91v=C3=A1g=C3=B3" writes: > On 2019-09-23 15:08, Markus Armbruster wrote: >> "K=C5=91v=C3=A1g=C3=B3, Zolt=C3=A1n" writes: >> >>> This will allow us to disable mixeng when we use a decent backend. >>> >>> Disabling mixeng have a few advantages: >>> * we no longer convert the audio output from one format to another, when >>> the underlying audio system would just convert it to a third format. >>> We no longer convert, only the underlying system, when needed. >>> * the underlying system probably has better resampling and sample format >>> converting methods anyway... >>> * we may support formats that the mixeng currently does not support (S24 >>> or float samples, more than two channels) >>> * when using an audio server (like pulseaudio) different sound card >>> outputs will show up as separate streams, even if we use only one >>> backend >>> >>> Disadvantages: >>> * audio capturing no longer works (wavcapture, and vnc audio extension) >>> * some backends only support a single playback stream or very picky >>> about the audio format. In this case we can't disable mixeng. >>> >>> However mixeng is not removed, only made optional, so this shouldn't be >>> a big concern. >>> >>> Signed-off-by: K=C5=91v=C3=A1g=C3=B3, Zolt=C3=A1n >>> --- >>> >>> Notes: >>> Changes from v1: >>> * renamed mixeng to mixing-engine >>> >>> qapi/audio.json | 5 +++++ >>> qemu-options.hx | 6 ++++++ >>> 2 files changed, 11 insertions(+) >>> >>> diff --git a/qapi/audio.json b/qapi/audio.json >>> index 9fefdf5186..0535eff794 100644 >>> --- a/qapi/audio.json >>> +++ b/qapi/audio.json >>> @@ -11,6 +11,10 @@ >>> # General audio backend options that are used for both playback and >>> # recording. >>> # >>> +# @mixing-engine: use QEMU's mixing engine to mix all streams inside Q= EMU. When >>> +# set to off, fixed-settings must be also off. Not eve= ry backend >>> +# compatible with the off setting (default on, since 4= .2) >>> +# >> >> Last sentence no verb. >> >> Which backends are compatible? > > Actually that's a simplification, it depends on a few things. When > mixeng is off, qemu will try to use the same format as the emulated > sound card, and if the backend doesn't support that format, it won't > work (no audio). Also attaching multiple sound cards to the same > audiodev might not work, if the backend doesn't support multiple > playback streams. If you use pulseaudio, it'll work without problems, > if you use alsa, it depends on your device. If you use a hw: device > directly, you'll likely only be able to use one emulated sound card > with a few selected audio formats. If you use dmix: (and plug), alsa > will handle the conversion and mixing, so it will work no matter what > format the emulated sound card uses. With OSS the situation is > probably similar, it depends on the kernel/hw what works and what not. > wav and spice certainly doesn't support multiple streams. I'm not > completely sure about the other backends right now, but I think dsound > and coreaudio can handle the necessary sample format conversions and > mixing. > >> What happens when you try the off setting with incompatible backends? > See above. What happens *exactly*? I'm asking because I'm concerned about the user experience. When a user asks for a combination of things QEMU can't provide, such as mixeng off with an incompatible backend, QEMU should fail with a suitable error message. Does it? Sometimes rejecting non-working configurations is impractical. Is it here? If yes, we should call out the problematic configurations in documentation. [...]