linux-kernel - Re: [PATCH v15 00/16] Add audio support in v4l2 framework

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Date: Fri, 3 May 2024 10:47:19 +0900
From: Mark Brown <broonie@...nel.org>
To: Mauro Carvalho Chehab <mchehab@...nel.org>
Cc: Takashi Iwai <tiwai@...e.de>,
	Sebastian Fricke <sebastian.fricke@...labora.com>,
	Shengjiu Wang <shengjiu.wang@....com>, hverkuil@...all.nl,
	sakari.ailus@....fi, tfiga@...omium.org, m.szyprowski@...sung.com,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	shengjiu.wang@...il.com, Xiubo.Lee@...il.com, festevam@...il.com,
	nicoleotsuka@...il.com, lgirdwood@...il.com, perex@...ex.cz,
	tiwai@...e.com, alsa-devel@...a-project.org,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v15 00/16] Add audio support in v4l2 framework

On Thu, May 02, 2024 at 10:26:43AM +0100, Mauro Carvalho Chehab wrote:
> Mauro Carvalho Chehab <mchehab@...nel.org> escreveu:

> > There are still time control associated with it, as audio and video
> > needs to be in sync. This is done by controlling the buffers size 
> > and could be fine-tuned by checking when the buffer transfer is done.

...

> Just complementing: on media, we do this per video buffer (or
> per half video buffer). A typical use case on cameras is to have
> buffers transferred 30 times per second, if the video was streamed 
> at 30 frames per second. 

IIRC some big use case for this hardware was transcoding so there was a
desire to just go at whatever rate the hardware could support as there
is no interactive user consuming the output as it is generated.

> I would assume that, on an audio/video stream, the audio data
> transfer will be programmed to also happen on a regular interval.

With audio the API is very much "wake userspace every Xms".

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