From: Vanessa Ezekowitz <vanessaezekowitz@gmail.com>
To: video4linux-list@redhat.com
Subject: Re: [PATCH 0 of 9] videobuf fixes
Date: Sat, 29 Mar 2008 17:49:10 -0500 [thread overview]
Message-ID: <200803291749.10451.vanessaezekowitz@gmail.com> (raw)
In-Reply-To: <20080329052559.GA4470@plankton.ifup.org>
On Saturday 29 March 2008 12:25:59 am Brandon Philips wrote:
> > I've opened 3 mplayer windows, reading /dev/video0. I closed the second one and
> > opened again. I got an error:
>
> Shouldn't V4L2 devices not be able to stream to multiple applications at
> once? Quoting the spec:
I'm not exactly on top of current driver development, so I apologize if this response if misdirected.
I disagree with the proposal.
In certain instances, it is desirable for more than one application at a time to read from a stream (provided both are receiving the exact same stream, i.e. without lost/duplicate frames). The case could be argued that one may want to use a command-line tool set like mjpegtools and ffmpeg to record a stream, while using xawtv to view the stream. In point of fact, I've done this myself and have found it incredibly handy.
I can see how it would be especially useful on machines with fewer resources than are needed for complex applications like mythtv.
> "V4L2 drivers should not support multiple applications reading or
> writing the same data stream on a device by copying buffers, time
> multiplexing or similar means. This is better handled by a proxy
> application in user space. When the driver supports stream sharing
> anyway it must be implemented transparently. The V4L2 API does not
> specify how conflicts are solved."
Rather that lose a useful capability, why not just extend the spec to allow for it (and the potential error condition of course)? It's not as though all of the applications prior to this would suddenly stop working once you do.
--
"Life is full of happy and sad events. If you take the time
to concentrate on the former, you'll get further in life."
Vanessa Ezekowitz <vanessaezekowitz@gmail.com>
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next prev parent reply other threads:[~2008-03-29 22:51 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-28 10:18 [PATCH 0 of 9] videobuf fixes Brandon Philips
2008-03-28 10:18 ` [PATCH 1 of 9] soc_camera: Introduce a spinlock for use with videobuf Brandon Philips
2008-03-28 20:53 ` Guennadi Liakhovetski
2008-03-29 3:59 ` Brandon Philips
2008-04-04 13:46 ` [PATCH] soc-camera: use a spinlock for videobuffer queue Guennadi Liakhovetski
2008-04-04 20:17 ` Brandon Philips
2008-03-28 10:18 ` [PATCH 2 of 9] videobuf: Require spinlocks for all videobuf users Brandon Philips
2008-03-28 10:18 ` [PATCH 3 of 9] videobuf: Wakeup queues after changing the state to ERROR Brandon Philips
2008-03-28 10:18 ` [PATCH 4 of 9] videobuf: Simplify videobuf_waiton logic and possibly avoid missed wakeup Brandon Philips
2008-03-28 10:18 ` [PATCH 5 of 9] videobuf-vmalloc.c: Remove buf_release from videobuf_vm_close Brandon Philips
2008-03-28 10:18 ` [PATCH 6 of 9] videobuf-vmalloc.c: Fix hack of postponing mmap on remap failure Brandon Philips
[not found] ` <20080405131236.7c083554@gaivota>
[not found] ` <20080406080011.GA3596@plankton.ifup.org>
[not found] ` <20080407183226.703217fc@gaivota>
[not found] ` <20080408152238.GA8438@plankton.public.utexas.edu>
2008-04-08 18:40 ` Mauro Carvalho Chehab
[not found] ` <c8b4dbe10804081306xb1e8f91q64d1e6d18d3d2531@mail.gmail.com>
2008-04-08 20:50 ` Mauro Carvalho Chehab
[not found] ` <c8b4dbe10804090626l6b2b10d9p1c22e02dfe2850fe@mail.gmail.com>
2008-04-09 20:42 ` Mauro Carvalho Chehab
[not found] ` <20080408204514.GA6844@plankton.public.utexas.edu>
2008-04-08 21:37 ` Mauro Carvalho Chehab
[not found] ` <20080415021558.GA22068@plankton.ifup.org>
2008-04-15 14:10 ` Mauro Carvalho Chehab
2008-03-28 10:18 ` [PATCH 7 of 9] vivi: Simplify the vivi driver and avoid deadlocks Brandon Philips
2008-03-28 18:34 ` Mauro Carvalho Chehab
2008-03-29 5:35 ` Brandon Philips
2008-03-31 19:35 ` Mauro Carvalho Chehab
2008-03-28 10:18 ` [PATCH 8 of 9] videobuf: Avoid deadlock with QBUF and bring up to spec for empty queue Brandon Philips
2008-03-28 10:18 ` [PATCH 9 of 9] videobuf-dma-sg.c: Avoid NULL dereference and add comment about backwards compatibility Brandon Philips
2008-03-28 19:09 ` [PATCH 0 of 9] videobuf fixes Mauro Carvalho Chehab
2008-03-29 5:25 ` Brandon Philips
2008-03-29 22:49 ` Vanessa Ezekowitz [this message]
2008-03-31 18:35 ` Mauro Carvalho Chehab
2008-03-31 19:26 ` Brandon Philips
2008-03-31 21:31 ` Mauro Carvalho Chehab
2008-04-01 3:11 ` Brandon Philips
2008-04-01 20:49 ` Mauro Carvalho Chehab
2008-04-02 18:54 ` Brandon Philips
2008-04-02 20:06 ` Mauro Carvalho Chehab
2008-04-02 18:56 ` Brandon Philips
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