[media-workshop] Agenda for the Edinburgh mini-summit

Hans Verkuil hverkuil at xs4all.nl
Tue Sep 10 09:54:38 CEST 2013

On Tue 10 September 2013 09:36:00 Hugues FRUCHET wrote:
> Thanks Hans,
> Have you some implementation based on meta that we can check to see code details ?

Not as such. Basically you just add another pixelformat define for a multiplanar
format. And you define this format as having X video planes and Y planes containing
meta data.

> It would be nice to have one with noticeable amount of code/processing made on user-land side.
> I'm wondering also how libv4l is selecting each driver specific user-land plugin and how they are loaded.

libv4l-mplane in v4l-utils.git is an example of a plugin.

Documentation on the plugin API seems to be sparse, but Hans de Goede,
Sakari Ailus or Laurent Pinchart know a lot more about it.

There are (to my knowledge) no plugins that do exactly what you want, so
you're the first. But it has been designed with your use-case in mind.



> BR.
> -----Original Message-----
> From: Hans Verkuil [mailto:hverkuil at xs4all.nl] 
> Sent: lundi 9 septembre 2013 12:33
> To: Hugues FRUCHET
> Cc: Mauro Carvalho Chehab; Oliver Schinagl; media-workshop; Benjamin Gaignard; linux-media at vger.kernel.org
> Subject: Re: [media-workshop] Agenda for the Edinburgh mini-summit
> Hi Hugues,
> On 09/05/2013 01:37 PM, Hugues FRUCHET wrote:
> > Hi Mauro,
> > 
> > For floating point issue, we have not encountered such issue while
> > integrating various codec (currently H264, MPEG4, VP8 of both Google
> > G1 IP & ST IPs), could you precise which codec you experienced which
> > required FP support ?
> > 
> > For user-space library, problem we encountered is that interface
> > between parsing side (for ex. H264 SPS/PPS decoding, slice header
> > decoding, references frame list management, ...moreover all that is
> > needed to prepare hardware IPs call) and decoder side (hardware IPs
> > handling) is not standardized and differs largely regarding IPs or
> > CPU/copro partitioning. This means that even if we use the standard
> > V4L2 capture interface to inject video bitstream (H264 access units
> > for ex), some proprietary meta are needed to be attached to each
> > buffers, making de facto "un-standard" the V4L2 interface for this
> > driver.
> There are lots of drivers (mostly camera drivers) that have non-standard
> video formats. That's perfectly fine, as long as libv4l plugins/conversions
> exist to convert it to something that's standardized.
> Any application using libv4l doesn't notice the work going on under the
> hood and it will look like a standard v4l2 driver.
> The multiplanar API seems to me to be very suitable for these sort of devices.
> > Exynos S5P MFC is not attaching any meta to capture input
> > buffers, keeping a standard video bitstream injection interface (what
> > is output naturally by well-known standard demuxers such as gstreamer
> > ones or Android Stagefright ones). This is the way we want to go, we
> > will so keep hardware details at kernel driver side. On the other
> > hand, this simplify drastically the integration of our video drivers
> > on user-land multimedia middleware, reducing the time to market and
> > support needed when reaching our end-customers. Our target is to
> > create a unified gstreamer V4L2 decoder(encoder) plugin and a unified
> > OMX V4L2 decoder(encoder) to fit Android, based on a single V4L2 M2M
> > API whatever hardware IP is.
> > 
> > About mini summit, Benjamin and I are checking internally how to
> > attend to discuss this topic. We think that about half a day is
> > needed to discuss this, we can so share our code and discuss about
> > other codebase you know dealing with video codecs.> 
> We are getting a lot of topics for the agenda and half a day for one topic
> seems problematic to me.
> One option is to discuss this in a smaller group a day earlier (October 22).
> We might be able to get a room, or we can discuss it in the hotel lounge or
> pub :-) or something.
> Another option is that ST organizes a separate brainstorm session with a
> few core developers. We done that in the past quite successfully.
> Regards,
> 	Hans

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