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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BF3C0C76188 for ; Fri, 19 Jul 2019 05:45:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 686DE2082F for ; Fri, 19 Jul 2019 05:45:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="eGCR0Fig" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727093AbfGSFpy (ORCPT ); Fri, 19 Jul 2019 01:45:54 -0400 Received: from mail-ed1-f67.google.com ([209.85.208.67]:32932 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726773AbfGSFpy (ORCPT ); Fri, 19 Jul 2019 01:45:54 -0400 Received: by mail-ed1-f67.google.com with SMTP id i11so33396460edq.0 for ; Thu, 18 Jul 2019 22:45:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=07pJ3nyuuSc07oWggqAbYmP3KjrWKt7fIOEkaSGmZv8=; b=eGCR0FigA28d1QM9Yl5AmYmEApYf782jdUGuq8uZJn/PqFYxEThDZPnMc8Unh6+KUe dSxlcp7pXXBEmeppylAuecxMB5mauy5xN/HbrHzzyM965K3yxh3te6IS22IIMaGJZIay MUQ1OstBmdfZKAagPPLJcH7w049xrv9kNpiw0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=07pJ3nyuuSc07oWggqAbYmP3KjrWKt7fIOEkaSGmZv8=; b=NuBWwwNzFKEfpTLVZucjw9hi2uK6jjmxtxuBlKIzT+SxYjfa1zeIWn6nqk/SkteAsG 1UPTTwXZiQyjx062u9dYueY+lv/ef6EQvjVjLFmmo9tXda5cFSgvcu+8mGZ0fnqNweqL hTOxe/aGtutcc1mOuwgQJRvGCUc7NVtUnV26mT3zyji4+3522Xovsw4AAwu/cFYenu5Z OyjIbSm11P6jMY6B3mcCrryhLSaaTUHvKorv92SjNzLq4Gfn6lqz/xGgRcf+H3Syd72D nwRBb/rpBT+1ioAVYHrlPZnE/JQOptH538Iwgmtf7ASlVJ4YZcgjx52NSK1uHkKV6IGC kz/Q== X-Gm-Message-State: APjAAAXWT6qAfD2EsvjQw98435GJjVl/qKNg48uKPzmuabBcS6CIXOlK UkvLawHz9L89dwkS4vfrR+9AYxzaYz3mWA== X-Google-Smtp-Source: APXvYqyp4X56XLDIYj3cEVh8uyN2wmzhW51D+yIiOacz/YrzwAraaciXCP4d5Ylf1qvvfsdP7atO1Q== X-Received: by 2002:a17:906:cd1f:: with SMTP id oz31mr39087952ejb.226.1563515149510; Thu, 18 Jul 2019 22:45:49 -0700 (PDT) Received: from mail-wr1-f42.google.com (mail-wr1-f42.google.com. [209.85.221.42]) by smtp.gmail.com with ESMTPSA id a8sm8044697edt.56.2019.07.18.22.45.47 for (version=TLS1_3 cipher=AEAD-AES128-GCM-SHA256 bits=128/128); Thu, 18 Jul 2019 22:45:48 -0700 (PDT) Received: by mail-wr1-f42.google.com with SMTP id g17so30956291wrr.5 for ; Thu, 18 Jul 2019 22:45:47 -0700 (PDT) X-Received: by 2002:adf:ed41:: with SMTP id u1mr51378709wro.162.1563515147179; Thu, 18 Jul 2019 22:45:47 -0700 (PDT) MIME-Version: 1.0 References: <20190603112835.19661-1-hverkuil-cisco@xs4all.nl> <20190603112835.19661-2-hverkuil-cisco@xs4all.nl> <4feacf8e6c5389ee0a3ff5e9b8611b05f6592c3c.camel@ndufresne.ca> In-Reply-To: <4feacf8e6c5389ee0a3ff5e9b8611b05f6592c3c.camel@ndufresne.ca> From: Tomasz Figa Date: Fri, 19 Jul 2019 14:45:33 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCHv4 1/2] media: docs-rst: Document memory-to-memory video decoder interface To: Nicolas Dufresne Cc: Hans Verkuil , Linux Media Mailing List , Linux Kernel Mailing List , Alexandre Courbot , Philipp Zabel , Stanimir Varbanov , Andrew-CT Chen , Tiffany Lin , Pawel Osciak Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Wed, Jul 17, 2019 at 9:18 PM Nicolas Dufresne wro= te: > > Hello, > > there is one little detail/proposal, see inline . > > Le lundi 03 juin 2019 =C3=A0 13:28 +0200, Hans Verkuil a =C3=A9crit : > > From: Tomasz Figa > > > > Due to complexity of the video decoding process, the V4L2 drivers of > > stateful decoder hardware require specific sequences of V4L2 API calls > > to be followed. These include capability enumeration, initialization, > > decoding, seek, pause, dynamic resolution change, drain and end of > > stream. > > > > Specifics of the above have been discussed during Media Workshops at > > LinuxCon Europe 2012 in Barcelona and then later Embedded Linux > > Conference Europe 2014 in D=C3=BCsseldorf. The de facto Codec API that > > originated at those events was later implemented by the drivers we alre= ady > > have merged in mainline, such as s5p-mfc or coda. > > > > The only thing missing was the real specification included as a part of > > Linux Media documentation. Fix it now and document the decoder part of > > the Codec API. > > > > Signed-off-by: Tomasz Figa > > Signed-off-by: Hans Verkuil > > --- > > Documentation/media/uapi/v4l/dev-decoder.rst | 1084 +++++++++++++++++ > > Documentation/media/uapi/v4l/dev-mem2mem.rst | 8 +- > > Documentation/media/uapi/v4l/pixfmt-v4l2.rst | 5 + > > Documentation/media/uapi/v4l/v4l2.rst | 10 +- > > .../media/uapi/v4l/vidioc-decoder-cmd.rst | 41 +- > > 5 files changed, 1132 insertions(+), 16 deletions(-) > > create mode 100644 Documentation/media/uapi/v4l/dev-decoder.rst > > > > diff --git a/Documentation/media/uapi/v4l/dev-decoder.rst b/Documentati= on/media/uapi/v4l/dev-decoder.rst > > new file mode 100644 > > index 000000000000..b106f2d97c48 > > --- /dev/null > > +++ b/Documentation/media/uapi/v4l/dev-decoder.rst > > @@ -0,0 +1,1084 @@ > > +.. SPDX-License-Identifier: GPL-2.0 > > + > > +.. _decoder: > > + > > +************************************************* > > +Memory-to-memory Stateful Video Decoder Interface > > +************************************************* > > + > > +A stateful video decoder takes complete chunks of the bitstream (e.g. = Annex-B > > +H.264/HEVC stream, raw VP8/9 stream) and decodes them into raw video f= rames in > > +display order. The decoder is expected not to require any additional i= nformation > > +from the client to process these buffers. > > + > > +Performing software parsing, processing etc. of the stream in the driv= er in > > +order to support this interface is strongly discouraged. In case such > > +operations are needed, use of the Stateless Video Decoder Interface (i= n > > +development) is strongly advised. > > + > > +Conventions and notation used in this document > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +1. The general V4L2 API rules apply if not specified in this document > > + otherwise. > > + > > +2. The meaning of words "must", "may", "should", etc. is as per `RFC > > + 2119 `_. > > + > > +3. All steps not marked "optional" are required. > > + > > +4. :c:func:`VIDIOC_G_EXT_CTRLS` and :c:func:`VIDIOC_S_EXT_CTRLS` may b= e used > > + interchangeably with :c:func:`VIDIOC_G_CTRL` and :c:func:`VIDIOC_S_= CTRL`, > > + unless specified otherwise. > > + > > +5. Single-planar API (see :ref:`planar-apis`) and applicable structure= s may be > > + used interchangeably with multi-planar API, unless specified otherw= ise, > > + depending on decoder capabilities and following the general V4L2 gu= idelines. > > + > > +6. i =3D [a..b]: sequence of integers from a to b, inclusive, i.e. i = =3D > > + [0..2]: i =3D 0, 1, 2. > > + > > +7. Given an ``OUTPUT`` buffer A, then A=E2=80=99 represents a buffer o= n the ``CAPTURE`` > > + queue containing data that resulted from processing buffer A. > > + > > +.. _decoder-glossary: > > + > > +Glossary > > +=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +CAPTURE > > + the destination buffer queue; for decoders, the queue of buffers co= ntaining > > + decoded frames; for encoders, the queue of buffers containing an en= coded > > + bitstream; ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` or > > + ``V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE``; data is captured from the h= ardware > > + into ``CAPTURE`` buffers. > > + > > +client > > + the application communicating with the decoder or encoder implement= ing > > + this interface. > > + > > +coded format > > + encoded/compressed video bitstream format (e.g. H.264, VP8, etc.); = see > > + also: raw format. > > + > > +coded height > > + height for given coded resolution. > > + > > +coded resolution > > + stream resolution in pixels aligned to codec and hardware requireme= nts; > > + typically visible resolution rounded up to full macroblocks; > > + see also: visible resolution. > > + > > +coded width > > + width for given coded resolution. > > + > > +decode order > > + the order in which frames are decoded; may differ from display orde= r if the > > + coded format includes a feature of frame reordering; for decoders, > > + ``OUTPUT`` buffers must be queued by the client in decode order; fo= r > > + encoders ``CAPTURE`` buffers must be returned by the encoder in dec= ode order. > > + > > +destination > > + data resulting from the decode process; see ``CAPTURE``. > > + > > +display order > > + the order in which frames must be displayed; for encoders, ``OUTPUT= `` > > + buffers must be queued by the client in display order; for decoders= , > > + ``CAPTURE`` buffers must be returned by the decoder in display orde= r. > > + > > +DPB > > + Decoded Picture Buffer; an H.264/HEVC term for a buffer that stores= a decoded > > + raw frame available for reference in further decoding steps. > > + > > +EOS > > + end of stream. > > + > > +IDR > > + Instantaneous Decoder Refresh; a type of a keyframe in an H.264/HEV= C-encoded > > + stream, which clears the list of earlier reference frames (DPBs). > > + > > +keyframe > > + an encoded frame that does not reference frames decoded earlier, i.= e. > > + can be decoded fully on its own. > > + > > +macroblock > > + a processing unit in image and video compression formats based on l= inear > > + block transforms (e.g. H.264, VP8, VP9); codec-specific, but for mo= st of > > + popular codecs the size is 16x16 samples (pixels). > > + > > +OUTPUT > > + the source buffer queue; for decoders, the queue of buffers contain= ing > > + an encoded bitstream; for encoders, the queue of buffers containing= raw > > + frames; ``V4L2_BUF_TYPE_VIDEO_OUTPUT`` or > > + ``V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE``; the hardware is fed with dat= a > > + from ``OUTPUT`` buffers. > > + > > +PPS > > + Picture Parameter Set; a type of metadata entity in an H.264/HEVC b= itstream. > > + > > +raw format > > + uncompressed format containing raw pixel data (e.g. YUV, RGB format= s). > > + > > +resume point > > + a point in the bitstream from which decoding may start/continue, wi= thout > > + any previous state/data present, e.g.: a keyframe (VP8/VP9) or > > + SPS/PPS/IDR sequence (H.264/HEVC); a resume point is required to st= art decode > > + of a new stream, or to resume decoding after a seek. > > + > > +source > > + data fed to the decoder or encoder; see ``OUTPUT``. > > + > > +source height > > + height in pixels for given source resolution; relevant to encoders = only. > > + > > +source resolution > > + resolution in pixels of source frames being source to the encoder a= nd > > + subject to further cropping to the bounds of visible resolution; re= levant to > > + encoders only. > > + > > +source width > > + width in pixels for given source resolution; relevant to encoders o= nly. > > + > > +SPS > > + Sequence Parameter Set; a type of metadata entity in an H.264/HEVC = bitstream. > > + > > +stream metadata > > + additional (non-visual) information contained inside encoded bitstr= eam; > > + for example: coded resolution, visible resolution, codec profile. > > + > > +visible height > > + height for given visible resolution; display height. > > + > > +visible resolution > > + stream resolution of the visible picture, in pixels, to be used for > > + display purposes; must be smaller or equal to coded resolution; > > + display resolution. > > + > > +visible width > > + width for given visible resolution; display width. > > + > > +State machine > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +.. kernel-render:: DOT > > + :alt: DOT digraph of decoder state machine > > + :caption: Decoder state machine > > + > > + digraph decoder_state_machine { > > + node [shape =3D doublecircle, label=3D"Decoding"] Decoding; > > + > > + node [shape =3D circle, label=3D"Initialization"] Initializatio= n; > > + node [shape =3D circle, label=3D"Capture\nsetup"] CaptureSetup; > > + node [shape =3D circle, label=3D"Dynamic\nresolution\nchange"] = ResChange; > > + node [shape =3D circle, label=3D"Stopped"] Stopped; > > + node [shape =3D circle, label=3D"Drain"] Drain; > > + node [shape =3D circle, label=3D"Seek"] Seek; > > + node [shape =3D circle, label=3D"End of stream"] EoS; > > + > > + node [shape =3D point]; qi > > + qi -> Initialization [ label =3D "open()" ]; > > + > > + Initialization -> CaptureSetup [ label =3D "CAPTURE\nformat\nes= tablished" ]; > > + > > + CaptureSetup -> Stopped [ label =3D "CAPTURE\nbuffers\nready" ]= ; > > + > > + Decoding -> ResChange [ label =3D "Stream\nresolution\nchange" = ]; > > + Decoding -> Drain [ label =3D "V4L2_DEC_CMD_STOP" ]; > > + Decoding -> EoS [ label =3D "EoS mark\nin the stream" ]; > > + Decoding -> Seek [ label =3D "VIDIOC_STREAMOFF(OUTPUT)" ]; > > + Decoding -> Stopped [ label =3D "VIDIOC_STREAMOFF(CAPTURE)" ]; > > + Decoding -> Decoding; > > + > > + ResChange -> CaptureSetup [ label =3D "CAPTURE\nformat\nestabli= shed" ]; > > + ResChange -> Seek [ label =3D "VIDIOC_STREAMOFF(OUTPUT)" ]; > > + > > + EoS -> Drain [ label =3D "Implicit\ndrain" ]; > > + > > + Drain -> Stopped [ label =3D "All CAPTURE\nbuffers dequeued\nor= \nVIDIOC_STREAMOFF(CAPTURE)" ]; > > + Drain -> Seek [ label =3D "VIDIOC_STREAMOFF(OUTPUT)" ]; > > + > > + Seek -> Decoding [ label =3D "VIDIOC_STREAMON(OUTPUT)" ]; > > + Seek -> Initialization [ label =3D "VIDIOC_REQBUFS(OUTPUT, 0)" = ]; > > + > > + Stopped -> Decoding [ label =3D "V4L2_DEC_CMD_START\nor\nVIDIOC= _STREAMON(CAPTURE)" ]; > > + Stopped -> Seek [ label =3D "VIDIOC_STREAMOFF(OUTPUT)" ]; > > + } > > + > > +Querying capabilities > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +1. To enumerate the set of coded formats supported by the decoder, the > > + client may call :c:func:`VIDIOC_ENUM_FMT` on ``OUTPUT``. > > + > > + * The full set of supported formats will be returned, regardless of= the > > + format set on ``CAPTURE``. > > + > > +2. To enumerate the set of supported raw formats, the client may call > > + :c:func:`VIDIOC_ENUM_FMT` on ``CAPTURE``. > > + > > + * Only the formats supported for the format currently active on ``O= UTPUT`` > > + will be returned. > > + > > + * In order to enumerate raw formats supported by a given coded form= at, > > + the client must first set that coded format on ``OUTPUT`` and the= n > > + enumerate formats on ``CAPTURE``. > > + > > +3. The client may use :c:func:`VIDIOC_ENUM_FRAMESIZES` to detect suppo= rted > > + resolutions for a given format, passing desired pixel format in > > + :c:type:`v4l2_frmsizeenum` ``pixel_format``. > > + > > + * Values returned by :c:func:`VIDIOC_ENUM_FRAMESIZES` for a coded p= ixel > > + format will include all possible coded resolutions supported by t= he > > + decoder for given coded pixel format. > > + > > + * Values returned by :c:func:`VIDIOC_ENUM_FRAMESIZES` for a raw pix= el format > > + will include all possible frame buffer resolutions supported by t= he > > + decoder for given raw pixel format and the coded format currently= set on > > + ``OUTPUT``. > > + > > +4. Supported profiles and levels for the coded format currently set on > > + ``OUTPUT``, if applicable, may be queried using their respective co= ntrols > > + via :c:func:`VIDIOC_QUERYCTRL`. > > + > > +Initialization > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +1. Set the coded format on ``OUTPUT`` via :c:func:`VIDIOC_S_FMT` > > + > > + * **Required fields:** > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > + > > + ``pixelformat`` > > + a coded pixel format. > > + > > + ``width``, ``height`` > > + coded resolution of the stream; required only if it cannot be= parsed > > + from the stream for the given coded format; otherwise the dec= oder will > > + use this resolution as a placeholder resolution that will lik= ely change > > + as soon as it can parse the actual coded resolution from the = stream. > > + > > + ``sizeimage`` > > + desired size of ``OUTPUT`` buffers; the decoder may adjust it= to > > + match hardware requirements. > > + > > + other fields > > + follow standard semantics. > > + > > + * **Return fields:** > > + > > + ``sizeimage`` > > + adjusted size of ``OUTPUT`` buffers. > > + > > + * The ``CAPTURE`` format will be updated with an appropriate frame = buffer > > + resolution instantly based on the width and height returned by > > + :c:func:`VIDIOC_S_FMT`. > > + However, for coded formats that include stream resolution informa= tion, > > + after the decoder is done parsing the information from the stream= , it will > > + update the ``CAPTURE`` format with new values and signal a source= change > > + event, regardless of whether they match the values set by the cli= ent or > > + not. > > + > > + .. important:: > > + > > + Changing the ``OUTPUT`` format may change the currently set ``CA= PTURE`` > > + format. How the new ``CAPTURE`` format is determined is up to th= e decoder > > + and the client must ensure it matches its needs afterwards. > > + > > +2. Allocate source (bitstream) buffers via :c:func:`VIDIOC_REQBUFS` o= n > > + ``OUTPUT``. > > + > > + * **Required fields:** > > + > > + ``count`` > > + requested number of buffers to allocate; greater than zero. > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > + > > + ``memory`` > > + follows standard semantics. > > + > > + * **Return fields:** > > + > > + ``count`` > > + the actual number of buffers allocated. > > + > > + .. warning:: > > + > > + The actual number of allocated buffers may differ from the ``co= unt`` > > + given. The client must check the updated value of ``count`` aft= er the > > + call returns. > > + > > + Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``OUTPUT`` queu= e can be > > + used to have more control over buffer allocation. > > + > > + * **Required fields:** > > + > > + ``count`` > > + requested number of buffers to allocate; greater than zero. > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``OUTPUT``. > > + > > + ``memory`` > > + follows standard semantics. > > + > > + ``format`` > > + follows standard semantics. > > + > > + * **Return fields:** > > + > > + ``count`` > > + adjusted to the number of allocated buffers. > > + > > + .. warning:: > > + > > + The actual number of allocated buffers may differ from the ``co= unt`` > > + given. The client must check the updated value of ``count`` aft= er the > > + call returns. > > + > > +3. Start streaming on the ``OUTPUT`` queue via :c:func:`VIDIOC_STREAM= ON`. > > + > > +4. **This step only applies to coded formats that contain resolution = information > > + in the stream.** Continue queuing/dequeuing bitstream buffers to/f= rom the > > + ``OUTPUT`` queue via :c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQB= UF`. The > > + buffers will be processed and returned to the client in order, unt= il > > + required metadata to configure the ``CAPTURE`` queue are found. Th= is is > > + indicated by the decoder sending a ``V4L2_EVENT_SOURCE_CHANGE`` ev= ent with > > + ``changes`` set to ``V4L2_EVENT_SRC_CH_RESOLUTION``. > > + > > + * It is not an error if the first buffer does not contain enough d= ata for > > + this to occur. Processing of the buffers will continue as long a= s more > > + data is needed. > > + > > + * If data in a buffer that triggers the event is required to decod= e the > > + first frame, it will not be returned to the client, until the > > + initialization sequence completes and the frame is decoded. > > + > > + * If the client has not set the coded resolution of the stream on = its own, > > + calling :c:func:`VIDIOC_G_FMT`, :c:func:`VIDIOC_S_FMT`, > > + :c:func:`VIDIOC_TRY_FMT` or :c:func:`VIDIOC_REQBUFS` on the ``CA= PTURE`` > > + queue will not return the real values for the stream until a > > + ``V4L2_EVENT_SOURCE_CHANGE`` event is signaled. > > + > > + .. important:: > > + > > + Any client query issued after the decoder queues the event will= return > > + values applying to the just parsed stream, including queue form= ats, > > + selection rectangles and controls. > > + > > + .. note:: > > + > > + A client capable of acquiring stream parameters from the bitstr= eam on > > + its own may attempt to set the width and height of the ``OUTPUT= `` format > > + to non-zero values matching the coded size of the stream, skip = this step > > + and continue with the `Capture setup` sequence. However, it mus= t not > > + rely on any driver queries regarding stream parameters, such as > > + selection rectangles and controls, since the decoder has not pa= rsed them > > + from the stream yet. If the values configured by the client do = not match > > + those parsed by the decoder, a `Dynamic resolution change` will= be > > + triggered to reconfigure them. > > + > > + .. note:: > > + > > + No decoded frames are produced during this phase. > > + > > +5. Continue with the `Capture setup` sequence. > > + > > +Capture setup > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +1. Call :c:func:`VIDIOC_G_FMT` on the ``CAPTURE`` queue to get format= for the > > + destination buffers parsed/decoded from the bitstream. > > + > > + * **Required fields:** > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + * **Return fields:** > > + > > + ``width``, ``height`` > > + frame buffer resolution for the decoded frames. > > + > > + ``pixelformat`` > > + pixel format for decoded frames. > > + > > + ``num_planes`` (for _MPLANE ``type`` only) > > + number of planes for pixelformat. > > + > > + ``sizeimage``, ``bytesperline`` > > + as per standard semantics; matching frame buffer format. > > + > > + .. note:: > > + > > + The value of ``pixelformat`` may be any pixel format supported = by the > > + decoder for the current stream. The decoder should choose a > > + preferred/optimal format for the default configuration. For exa= mple, a > > + YUV format may be preferred over an RGB format if an additional > > + conversion step would be required for the latter. > > + > > +2. **Optional.** Acquire the visible resolution via > > + :c:func:`VIDIOC_G_SELECTION`. > > + > > + * **Required fields:** > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``target`` > > + set to ``V4L2_SEL_TGT_COMPOSE``. > > + > > + * **Return fields:** > > + > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > + the visible rectangle; it must fit within the frame buffer r= esolution > > + returned by :c:func:`VIDIOC_G_FMT` on ``CAPTURE``. > > + > > + * The following selection targets are supported on ``CAPTURE``: > > + > > + ``V4L2_SEL_TGT_CROP_BOUNDS`` > > + corresponds to the coded resolution of the stream. > > + > > + ``V4L2_SEL_TGT_CROP_DEFAULT`` > > + the rectangle covering the part of the ``CAPTURE`` buffer th= at > > + contains meaningful picture data (visible area); width and h= eight > > + will be equal to the visible resolution of the stream. > > + > > + ``V4L2_SEL_TGT_CROP`` > > + the rectangle within the coded resolution to be output to > > + ``CAPTURE``; defaults to ``V4L2_SEL_TGT_CROP_DEFAULT``; read= -only on > > + hardware without additional compose/scaling capabilities. > > + > > + ``V4L2_SEL_TGT_COMPOSE_BOUNDS`` > > + the maximum rectangle within a ``CAPTURE`` buffer, which the= cropped > > + frame can be composed into; equal to ``V4L2_SEL_TGT_CROP`` i= f the > > + hardware does not support compose/scaling. > > + > > + ``V4L2_SEL_TGT_COMPOSE_DEFAULT`` > > + equal to ``V4L2_SEL_TGT_CROP``. > > + > > + ``V4L2_SEL_TGT_COMPOSE`` > > + the rectangle inside a ``CAPTURE`` buffer into which the cro= pped > > + frame is written; defaults to ``V4L2_SEL_TGT_COMPOSE_DEFAULT= ``; > > + read-only on hardware without additional compose/scaling cap= abilities. > > + > > + ``V4L2_SEL_TGT_COMPOSE_PADDED`` > > + the rectangle inside a ``CAPTURE`` buffer which is overwritt= en by the > > + hardware; equal to ``V4L2_SEL_TGT_COMPOSE`` if the hardware = does not > > + write padding pixels. > > + > > + .. warning:: > > + > > + The values are guaranteed to be meaningful only after the decod= er > > + successfully parses the stream metadata. The client must not re= ly on the > > + query before that happens. > > + > > +3. **Optional.** Enumerate ``CAPTURE`` formats via :c:func:`VIDIOC_EN= UM_FMT` on > > + the ``CAPTURE`` queue. Once the stream information is parsed and k= nown, the > > + client may use this ioctl to discover which raw formats are suppor= ted for > > + given stream and select one of them via :c:func:`VIDIOC_S_FMT`. > > + > > + .. important:: > > + > > + The decoder will return only formats supported for the currentl= y > > + established coded format, as per the ``OUTPUT`` format and/or s= tream > > + metadata parsed in this initialization sequence, even if more f= ormats > > + may be supported by the decoder in general. In other words, the= set > > + returned will be a subset of the initial query mentioned in the > > + `Querying capabilities` section. > > + > > + For example, a decoder may support YUV and RGB formats for reso= lutions > > + 1920x1088 and lower, but only YUV for higher resolutions (due t= o > > + hardware limitations). After parsing a resolution of 1920x1088 = or lower, > > + :c:func:`VIDIOC_ENUM_FMT` may return a set of YUV and RGB pixel= formats, > > + but after parsing resolution higher than 1920x1088, the decoder= will not > > + return RGB, unsupported for this resolution. > > + > > + However, subsequent resolution change event triggered after > > + discovering a resolution change within the same stream may swit= ch > > + the stream into a lower resolution and :c:func:`VIDIOC_ENUM_FMT= ` > > + would return RGB formats again in that case. > > + > > +4. **Optional.** Set the ``CAPTURE`` format via :c:func:`VIDIOC_S_FMT= ` on the > > + ``CAPTURE`` queue. The client may choose a different format than > > + selected/suggested by the decoder in :c:func:`VIDIOC_G_FMT`. > > + > > + * **Required fields:** > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``pixelformat`` > > + a raw pixel format. > > + > > + * Setting the ``CAPTURE`` format will reset the compose selection r= ectangles > > + to their default values, based on the new resolution, as describe= d in the > > + previous step. > > + > > +5. **Optional.** Set the compose rectangle via :c:func:`VIDIOC_S_SELEC= TION` on > > + the ``CAPTURE`` queue if it is desired and if the decoder has compo= se and/or > > + scaling capabilities. > > + > > + * **Required fields:** > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``target`` > > + set to ``V4L2_SEL_TGT_COMPOSE``. > > + > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > + the rectangle inside a ``CAPTURE`` buffer into which the crop= ped > > + frame is written; defaults to ``V4L2_SEL_TGT_COMPOSE_DEFAULT`= `; > > + read-only on hardware without additional compose/scaling capa= bilities. > > + > > + * **Return fields:** > > + > > + ``r.left``, ``r.top``, ``r.width``, ``r.height`` > > + the visible rectangle; it must fit within the frame buffer re= solution > > + returned by :c:func:`VIDIOC_G_FMT` on ``CAPTURE``. > > + > > + .. warning:: > > + > > + The decoder may adjust the compose rectangle to the nearest > > + supported one to meet codec and hardware requirements. The clien= t needs > > + to check the adjusted rectangle returned by :c:func:`VIDIOC_S_SE= LECTION`. > > + > > +6. If all the following conditions are met, the client may resume the= decoding > > + instantly: > > + > > + * ``sizeimage`` of the new format (determined in previous steps) i= s less > > + than or equal to the size of currently allocated buffers, > > + > > + * the number of buffers currently allocated is greater than or equ= al to the > > + minimum number of buffers acquired in previous steps. To fulfill= this > > + requirement, the client may use :c:func:`VIDIOC_CREATE_BUFS` to = add new > > + buffers. > > + > > + In that case, the remaining steps do not apply and the client may = resume > > + the decoding by one of the following actions: > > + > > + * if the ``CAPTURE`` queue is streaming, call :c:func:`VIDIOC_DECO= DER_CMD` > > + with the ``V4L2_DEC_CMD_START`` command, > > + > > + * if the ``CAPTURE`` queue is not streaming, call :c:func:`VIDIOC_= STREAMON` > > + on the ``CAPTURE`` queue. > > + > > + However, if the client intends to change the buffer set, to lower > > + memory usage or for any other reasons, it may be achieved by follo= wing > > + the steps below. > > + > > +7. **If the** ``CAPTURE`` **queue is streaming,** keep queuing and de= queuing > > + buffers on the ``CAPTURE`` queue until a buffer marked with the > > + ``V4L2_BUF_FLAG_LAST`` flag is dequeued. > > + > > +8. **If the** ``CAPTURE`` **queue is streaming,** call :c:func:`VIDIO= C_STREAMOFF` > > + on the ``CAPTURE`` queue to stop streaming. > > + > > + .. warning:: > > + > > + The ``OUTPUT`` queue must remain streaming. Calling > > + :c:func:`VIDIOC_STREAMOFF` on it would abort the sequence and t= rigger a > > + seek. > > + > > +9. **If the** ``CAPTURE`` **queue has buffers allocated,** free the `= `CAPTURE`` > > + buffers using :c:func:`VIDIOC_REQBUFS`. > > + > > + * **Required fields:** > > + > > + ``count`` > > + set to 0. > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``memory`` > > + follows standard semantics. > > + > > +10. Allocate ``CAPTURE`` buffers via :c:func:`VIDIOC_REQBUFS` on the > > + ``CAPTURE`` queue. > > + > > + * **Required fields:** > > + > > + ``count`` > > + requested number of buffers to allocate; greater than zero. > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``memory`` > > + follows standard semantics. > > + > > + * **Return fields:** > > + > > + ``count`` > > + actual number of buffers allocated. > > + > > + .. warning:: > > + > > + The actual number of allocated buffers may differ from the ``co= unt`` > > + given. The client must check the updated value of ``count`` aft= er the > > + call returns. > > + > > + .. note:: > > + > > + To allocate more than the minimum number of buffers (for pipeli= ne > > + depth), the client may query the ``V4L2_CID_MIN_BUFFERS_FOR_CAP= TURE`` > > + control to get the minimum number of buffers required, and pass= the > > + obtained value plus the number of additional buffers needed in = the > > + ``count`` field to :c:func:`VIDIOC_REQBUFS`. > > + > > + Alternatively, :c:func:`VIDIOC_CREATE_BUFS` on the ``CAPTURE`` que= ue can be > > + used to have more control over buffer allocation. For example, by > > + allocating buffers larger than the current ``CAPTURE`` format, fut= ure > > + resolution changes can be accommodated. > > + > > + * **Required fields:** > > + > > + ``count`` > > + requested number of buffers to allocate; greater than zero. > > + > > + ``type`` > > + a ``V4L2_BUF_TYPE_*`` enum appropriate for ``CAPTURE``. > > + > > + ``memory`` > > + follows standard semantics. > > + > > + ``format`` > > + a format representing the maximum framebuffer resolution to = be > > + accommodated by newly allocated buffers. > > + > > + * **Return fields:** > > + > > + ``count`` > > + adjusted to the number of allocated buffers. > > + > > + .. warning:: > > + > > + The actual number of allocated buffers may differ from the ``c= ount`` > > + given. The client must check the updated value of ``count`` af= ter the > > + call returns. > > + > > + .. note:: > > + > > + To allocate buffers for a format different than parsed from the= stream > > + metadata, the client must proceed as follows, before the metada= ta > > + parsing is initiated: > > + > > + * set width and height of the ``OUTPUT`` format to desired code= d resolution to > > + let the decoder configure the ``CAPTURE`` format appropriatel= y, > > + > > + * query the ``CAPTURE`` format using :c:func:`VIDIOC_G_FMT` and= save it > > + until this step. > > + > > + The format obtained in the query may be then used with > > + :c:func:`VIDIOC_CREATE_BUFS` in this step to allocate the buffe= rs. > > + > > +11. Call :c:func:`VIDIOC_STREAMON` on the ``CAPTURE`` queue to start d= ecoding > > + frames. > > + > > +Decoding > > +=3D=3D=3D=3D=3D=3D=3D=3D > > + > > +This state is reached after the `Capture setup` sequence finishes succ= essfully. > > +In this state, the client queues and dequeues buffers to both queues v= ia > > +:c:func:`VIDIOC_QBUF` and :c:func:`VIDIOC_DQBUF`, following the standa= rd > > +semantics. > > + > > +The content of the source ``OUTPUT`` buffers depends on the active cod= ed pixel > > +format and may be affected by codec-specific extended controls, as sta= ted in > > +the documentation of each format. > > + > > +Both queues operate independently, following the standard behavior of = V4L2 > > +buffer queues and memory-to-memory devices. In addition, the order of = decoded > > +frames dequeued from the ``CAPTURE`` queue may differ from the order o= f queuing > > +coded frames to the ``OUTPUT`` queue, due to properties of the selecte= d coded > > +format, e.g. frame reordering. > > + > > +The client must not assume any direct relationship between ``CAPTURE`` > > +and ``OUTPUT`` buffers and any specific timing of buffers becoming > > +available to dequeue. Specifically: > > + > > +* a buffer queued to ``OUTPUT`` may result in no buffers being produce= d > > + on ``CAPTURE`` (e.g. if it does not contain encoded data, or if only > > + metadata syntax structures are present in it), > > + > > +* a buffer queued to ``OUTPUT`` may result in more than one buffer pro= duced > > + on ``CAPTURE`` (if the encoded data contained more than one frame, o= r if > > + returning a decoded frame allowed the decoder to return a frame that > > + preceded it in decode, but succeeded it in the display order), > > + > > +* a buffer queued to ``OUTPUT`` may result in a buffer being produced = on > > + ``CAPTURE`` later into decode process, and/or after processing furth= er > > + ``OUTPUT`` buffers, or be returned out of order, e.g. if display > > + reordering is used, > > + > > +* buffers may become available on the ``CAPTURE`` queue without additi= onal > > + buffers queued to ``OUTPUT`` (e.g. during drain or ``EOS``), because= of the > > + ``OUTPUT`` buffers queued in the past whose decoding results are onl= y > > + available at later time, due to specifics of the decoding process. > > + > > +.. note:: > > + > > + To allow matching decoded ``CAPTURE`` buffers with ``OUTPUT`` buffe= rs they > > + originated from, the client can set the ``timestamp`` field of the > > + :c:type:`v4l2_buffer` struct when queuing an ``OUTPUT`` buffer. The > > + ``CAPTURE`` buffer(s), which resulted from decoding that ``OUTPUT``= buffer > > + will have their ``timestamp`` field set to the same value when dequ= eued. > > + > > + In addition to the straightforward case of one ``OUTPUT`` buffer pr= oducing > > + one ``CAPTURE`` buffer, the following cases are defined: > > + > > + * one ``OUTPUT`` buffer generates multiple ``CAPTURE`` buffers: the= same > > + ``OUTPUT`` timestamp will be copied to multiple ``CAPTURE`` buffe= rs. > > + > > + * multiple ``OUTPUT`` buffers generate one ``CAPTURE`` buffer: time= stamp of > > + the ``OUTPUT`` buffer queued last will be copied. > > I'd like to propose to change this into " timestamp of the OUTPUT > buffer queued first will be copied". The rationale is the following, if > you have an OUTPUT buffer that is unaligned in the following form: > > [ remaining | complete frame ] > > The remaining data is the last bits of the current frame. So it should > share a timestamp with the bits that came before. But then you have > another frame which by accident could fit entirely in your buffer. With > the last approach, it is not possible to give that frame a timestamp. > > The first approach fixes this problem. If there was a remaining on the > very first buffer, it will be dropped anyway, so it also work for this > case. This modification is aligned with MPEG TS container specification > which says the the timestamp of the packet applies to the first ES > packet that starts, the remaining bits will reuse the previous packet > timestamp. The rest is common sense, e.g. the same ES packet should > only have one timestamp etc. Wouldn't that replace one problem with another? How about the case below? [ complete frame | partial frame ] [ remaining ] Best regards, Tomasz