On Fri, Sep 27, 2019 at 12:28 AM Nicolas Dufresne <nicolas@xxxxxxxxxxxx> wrote: > > Le jeudi 26 septembre 2019 à 19:21 +0900, Tomasz Figa a écrit : > > On Mon, Sep 23, 2019 at 11:13 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > > > Hi all, > > > > > > Since we have three separate half-day sessions for different topics I decided > > > to split the announcement for this in three emails as well, so these things > > > can be discussed in separate threads. > > > > > > All sessions are in room Terreaux VIP Lounge - Level 0. > > > There is a maximum of 15 people. > > > > > > The first session deals with the codec API and is on Tuesday morning from > > > 8:30 (tentative, might change) to 12:00 (we have to vacate the room at that > > > time). > > > > > > Confirmed attendees for this session: > > > > > > Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> > > > Alexandre Courbot <acourbot@xxxxxxxxxxxx> > > > Nicolas Dufresne <nicolas@xxxxxxxxxxxx> > > > Tomasz Figa <tfiga@xxxxxxxxxxxx> > > > Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx> > > > Daniel Gomez <daniel@xxxxxxxx> > > > Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx> > > > Eugen Hristev <Eugen.Hristev@xxxxxxxxxxxxx> > > > Paul Kocialkowski <paul.kocialkowski@xxxxxxxxxxx> > > > Helen Koike <helen.koike@xxxxxxxxxxxxx> > > > Michael Tretter <m.tretter@xxxxxxxxxxxxxx> > > > Hans Verkuil <hverkuil@xxxxxxxxx> > > > > > > Tentative: > > > > > > Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > Jacopo Mondi <jacopo@xxxxxxxxxx> > > > > > > Jacopo, please confirm if you want to attend this session. I didn't find > > > an email with explicit confirmation, so it was probably done via irc. But since > > > this session is getting close to capacity I would prefer to keep attendance to > > > those are actually working with codecs (or will work with it in the near future). > > > > > > If I missed someone, or you are on the list but won't attend after all, then > > > please let me know. > > > > > > > > > > > > Agenda: > > > > > > - Status of any pending patches related to codec support. > > > > > > - Requirements of moving codec drivers out of staging. > > > > > > - Finalize the stateful encoder API. There are two pieces that need > > > to be defined: > > > > > > 1) Setting the frame rate so bitrate control can make sense, since > > > they need to know this information. This is also relevant for the > > > stateless codec (and this may have to change on a per-frame basis > > > for stateless codecs!). > > > > > > This can either be implemented via ENUM_FRAMEINTERVALS for the coded > > > pixelformats and S_PARM support, or we just add a new control for this. > > > E.g. V4L2_CID_MPEG_VIDEO_FRAME_INTERVAL (or perhaps FRAME_RATE). If we > > > go for a control, then we need to consider the unit. We can use a > > > fraction as well. See this series that puts in the foundation for that: > > > https://patchwork.linuxtv.org/cover/58857/ > > > > > > I am inclined to go with a control, since the semantics don't really > > > match ENUM_FRAMEINTERVALS/S_PARM. These ioctls still need to be supported > > > for legacy drivers. Open question: some drivers (mediatek, hva, coda) > > > require S_PARM(OUTPUT), some (venus) allow both S_PARM(CAPTURE) and > > > S_PARM(OUTPUT). I am inclined to allow both since this is not a CAPTURE > > > vs OUTPUT thing, it is global to both queues. > > > > > > 2) Interactions between OUTPUT and CAPTURE formats. > > > > > > The main problem is what to do if the capture sizeimage is too small > > > for the OUTPUT resolution when streaming starts. > > > > > > Proposal: width and height of S_FMT(OUTPUT) are used to > > > calculate a minimum sizeimage (app may request more). This is > > > driver-specific. (Is it? Or is this codec-specific?) > > > > > > V4L2_FMT_FLAG_FIXED_RESOLUTION is always set for codec formats > > > for the encoder (i.e. we don't support mid-stream resolution > > > changes for now) and V4L2_EVENT_SOURCE_CHANGE is not > > > supported. See https://patchwork.linuxtv.org/patch/56478/ for > > > the patch adding this flag. > > > > > > Of course, if we start to support mid-stream resolution > > > changes (or other changes that require a source change event), > > > then this flag should be dropped by the encoder driver and > > > documentation on how to handle the source change event should > > > be documented in the encoder spec. I prefer to postpone this > > > until we have an encoder than can actually do mid-stream > > > resolution changes. > > > > > > If sizeimage of the OUTPUT is too small for the CAPTURE > > > resolution and V4L2_EVENT_SOURCE_CHANGE is not supported, > > > then the second STREAMON (either CAPTURE or OUTPUT) will > > > return -ENOMEM since there is not enough memory to do the > > > encode. > > > > > > If V4L2_FMT_FLAG_FIXED_RESOLUTION is set (i.e. that should > > > be the case for all current encoders), then any bitrate controls > > > will be limited in range to what the current state (CAPTURE and > > > OUTPUT formats and frame rate) supports. > > > > > > - Stateless encoders? > > > > This could indeed be a good topic. The hantro driver currently only > > supports JPEG encoding, but the hardware also supports H.264 and VP8 > > at least. It, however, handles only the core parts of the encoding, > > i.e. generating the actual encoded frames (slices) without headers. It > > also doesn't do any bitrate control or scene change detection on its > > own and expects quality parameters (QP) or keyframe requests to come > > from the software. > > > > I'm not sure if there is any other hardware with similar constraints > > that could use V4L2, but I believe the Intel video encoder supported > > by VAAPI has a similar design. > > The bitrate adaption is mostly done inside the VAAPI driver on Intel > side, software of shaders (could also be in HW for other drivers, not > sure if it's different with VDBox, which is real HW, also advertised as > the Iris Low Power CODCE). Users of VAAPI will setup certain parameter > in a structure called VAEncMiscParameterRateControl, but there is no > per-frame or per-slice work from what I can see. > > Though, the encoded bits are similar, they come pretty raw, no > sps/pps/sei or anything, and no slice headers at all. This all being > generated in gstreamer-vaapi, and I suppose it's the same in FFMPEG or > Chromium ? > I don't know about VAAPI, but for the Rockchip encoder, we have a libv4l2 plugin [1] that generates various low level parameters for the encoder (like QP for bitrate control), generates sps/pps/sei/slice headers and formats the bitstream, so it looks like a regular stateful encoder for Chromium. The API between the encoder driver and the plugin is like a stateful encoder + a number of private controls. [1] https://chromium.googlesource.com/chromiumos/third_party/libv4lplugins/+/master/libv4l-rockchip_v2 > > > > > Best regards, > > Tomasz > > > > > - Anything else? (I have a feeling I missed a codec-related topic, but > > > I can't find it in my mailbox) > > > > > > Regards, > > > > > > Hans
