Instead of relying on the default colorimetry chosen by
gst_video_info_set_format(), set info.colorimetry from the
values returned by G_FMT. This allows decoders to propagate
their input colorimetry downstream.
https://bugzilla.gnome.org/show_bug.cgi?id=766383
Move the extraction of colorimetry parameters from struct v4l2_format and the
setting of the identity matrix for RGB formats into the function to avoid code
duplication.
https://bugzilla.gnome.org/show_bug.cgi?id=766383
gst_v4l2_probe_caps() returns the coded size, not the visible size. Subtract
the known padding from probed caps with the coded size before using them as
filter for caps negotiation with downstream elements.
https://bugzilla.gnome.org/show_bug.cgi?id=766382
The gst_v4l2_object_acquire_format() function is used by v4l2videodec to obtain
the currently set capture format. Since G_FMT returns the coded size, the
visible size needs to be obtained from the compose rectangle in order to
negotiate it with downstream elements. The G_CROP call hasn't worked on mem2mem
capture queues for a long time. Instead use the G_SELECTION call to obtain the
compose rectangle and only fall back to G_CROP for ancient kernels.
https://bugzilla.gnome.org/show_bug.cgi?id=766381
On modern kernels, the G/S_FMT ioctls will always fail using
V4L2_BUF_TYPE_VIDEO_OVERLAY with VFL_DIR_TX (e.g. real overlay out drivers)
since this is not the intented use (rather rx, according to v4l2 API doc).
Probably this is why the Video Output Overlay interface was created, so if
the driver advertises it we might as well use.
For old kernels (pre 2012) the old way might still work so keeping this for
compatibility.
https://bugzilla.gnome.org/show_bug.cgi?id=761165
Support for the updated V4L2_PIX_FMT_XRGB555 was added in commit
2538fee2fd however, when setting the format
for use in v4l2 ioctls, the old deprecated format is still used. Convert
this to the new accepted format type, as the preferred format.
https://bugzilla.gnome.org/show_bug.cgi?id=767300
v4l2src can cause an "infinite message loop" when a base control exposed as a
property is not provided by the device. In these cases, if in the warning message
handling for the bus, the GST_DEBUG_BIN_TO_DOT_FILE* category of functions are used,
the src lookup causes a new warning to be posted on the bus, causing a loop.
This patch changes the warning for these controls so they are not posted on the bus.
https://bugzilla.gnome.org/show_bug.cgi?id=758703
A device can support more than one colorspace for a given image
dimension and pixel format. So we have to probe all the supported
colorspace and not only rely on the default one. Otherwise we could end
up with negotiation failure if the caps colorimetry field don't match
the v4l2 device default one even if the v4l2 could support such
colorimetry.
This patch enable probing if colorspace for both capture and output
device. It really makes sense for output device since the colorspace
shall be set by the application and a little less for capture device
which, at the moment, shall provide the colorspace; ie: the v4l2
specification seems to not take into account the fact that a capture
device could do colorspace conversion.
As a side effet, probing takes some times and so sligthly delay v4l2
initialization. Note that this patch only probe colorspace and not all
colorspace, matrix, transfer and range combination to avoid taking too
much time, especially with low-speed devices as full probing do 1782
ioctl.
https://bugzilla.gnome.org/show_bug.cgi?id=755937
gst_v4l2_object_get_caps_info() always return V4L2_PIX_FMT_SBGGR8
for all bayer formats. This is obviously broken if the device use
another ordering. Fix this by properly reading the format parameter.
https://bugzilla.gnome.org/show_bug.cgi?id=763318
Replicate V4L2_MAP_QUANTIZATION_DEFAULT macro behavior.
At #v4l it was described that documentation might be wrong and that
we should trust this macro instead.
https://bugzilla.gnome.org/show_bug.cgi?id=762529
Didn't know which one to choose between queuing and queueing, so I picked
the one with the biggest amount of vowels in a row ;-P (both are
acceptable apparently)
This time, check if it's an RGB format and sets the transformation
matrix to identity. The rest of the colorimetry information is
meaningfull and shall be kept.
https://bugzilla.gnome.org/show_bug.cgi?id=759624
Use the new primaries and transfer function for Adobe RGB.
Explicitly list the colorimetry instead of using the default GStreamer
ones. The defaults for BT2020, for example, do not match.
Explicitly set the matrix of SRGB to RGB.
Add properties to the device with exactly the same keys and sematics
as what pulseaudio uses as property keys.
Also handle the case when a device is probed manually and not through gudev.
https://bugzilla.gnome.org//show_bug.cgi?id=759780
This change add all the new RGB based format. Those format removes the
ambiguity with the ALPHA channel. Some other missing multiplanar format
has been added with some additional cleanup.
If GetStatus() fails, the status itself won't be very meaningful but we also
have to look at its return value. This fixes blocking pipelines when removing
sound devices or during other errors, where we wouldn't notice the error and
then wait forever.
https://bugzilla.gnome.org/show_bug.cgi?id=734098
If something in /dev/video* get added, removed or replaced, we need to
probe the devices again in order to ensure the dynamic devices are up to
date.
https://bugzilla.gnome.org/show_bug.cgi?id=758085
There was some miss-match in the implementation. This makes it
concistent, though functionally it worked, except the video decoder
output-io-mode getter.
These days the xserver seems to give us the same damage regions
over and over for entire windows, and we retrieve them multiple
times, which gives time for more damage to appear. Instead, just
quickly gather all damaged areas into a region list and copy
out once.
For 1ch or 2ch devices, we just need to set the caps to allow both
options since CoreAudio will up/downmix appropriately.
Also fixes the condition for the 2ch case to be exact, rather than at
least 2 channels since the downmix will not take place in the >stereo
case.
We need to initialize the AudioUnit early to be able to probe the
underlying device, but according to the AudioUnitInitialize() and
AudioUnitUninitialize() documentation, format changes should be done
while the AudioUnit is uninitialized. So we explicitly uninitialize the
AudioUnit during a format change and reinitialize it when we're done.
_audio_unit_property_listener is called either from a Core Audio thread
or as a result of a Core Audio API (e.g. AudioUnitInitialize)
from our own thread. In the latter case, osxbuf can be already locked
(GStreamer's mutex is not recursive).
We introduce the flag cached_caps_valid and use it instead of nullifying
cached_caps when we cannot lock on osxbuf.
https://bugzilla.gnome.org/show_bug.cgi?id=743758
- Probing caps is unified between source and sink
- Hardware stream format is now reported as preferred capabilities
(dynamically updated when hardware configuration changes)
- Get hardware channel layout from Remote IO just like from HAL
- More comprehensive mapping between AudioChannelLabel and
GstAudioChannelPosition
- Support for unpositioned channel layouts
- Announce stereo-mono upmixing/downmixing in caps
https://bugzilla.gnome.org/show_bug.cgi?id=743758
ximage metadata can't be transformed or copied, but provide an empty
transformation function instead of NULL to allow unconditional calling
of metas' transform functions.
https://bugzilla.gnome.org/show_bug.cgi?id=751778
AudioUnitGetProperty would fail with kParamErr (-50) every time,
simply because size wasn't initialized.
Now it returns zero latency, but at least it doesn't fail.
https://bugzilla.gnome.org/show_bug.cgi?id=750868
This fixes wrong mapping for sRGB as in GStreamer sRGB correctly
apply to RGB formats, while in V4L2 it's an alias for sYCC. Also
add support for the new quantization (range), ycbcr_encoding (matrix)
and xfer_func (transfer) enumeration.
This is the latest from media tree. This should enable more development
of the v4l2 elements. This includes new flags requires to fix draining
path in decoder, colorimetry and much more.
The v4l2 device restarts the sequence counter in case of streamoff/streamon,
the GST offset values are supposed to increment strictly monotonic, so
adjust the sequence counter/offset values in case of caps
renegotiation.
https://bugzilla.gnome.org/show_bug.cgi?id=745441
In case of v4l2 driver filled offset/sequence values add frame
loss detection (and write a warning message).
Move offset meta data setting and frame loss checking after the
timestamp adjustment code to get proper timestamps for the
warning message.
https://bugzilla.gnome.org/show_bug.cgi?id=745441
If propose_allocation() had not been called yet, it was possible that the driver was not asked at all.
In buffer pool: Consider minimum number of buffers requested by driver when setting config.
https://bugzilla.gnome.org/show_bug.cgi?id=746834
cocoawindow.m:339:5: error: 'NSOpenGLPFAWindow'
is deprecated: first deprecated in OS X 10.9
cocoawindow.m:576:7: error: 'NSOpenGLPFAFullScreen'
is deprecated: first deprecated in OS X 10.6
cocoawindow.m:605:24: error: 'setFullScreen'
is deprecated: first deprecated in OS X 10.7
Allow renegotiation to happen when buffers have returned after an allocation
query. As the allocation query is serialized, all buffers from the pool
should have returned and we can stop it to create a new one for the
new format
https://bugzilla.gnome.org/show_bug.cgi?id=682770
For output device, we should not update the buffer with flags and
timestamp when we dequeue. The information in the v4l2_buffer is not
meaningful and it breaks the case where the buffer is rendered at
multiple places.
https://bugzilla.gnome.org/show_bug.cgi?id=745438
The ringbuffer does allow renegotiation, so we do not have to report
fixed caps once it is acquired (based on a similar patch for the sink
side by Ilya Konstantinov <ilya.konstantinov@gmail.com>).
Once osxaudiosink's device is open, it fixates on the initial caps and
refuses to accept new caps. This is erroneous since the Audio Unit is
can accept a new ASBD, and GstAudioRingBuffer supports reconfiguration
as well.
https://bugzilla.gnome.org/show_bug.cgi?id=743925
Ensure gst_v4l2_buffer_pool_release_buffer() releases the associated
GstV4l2MemoryGroup. In particular, this allows for closing the DMABUF
handles prior to instantiating new ones.
https://bugzilla.gnome.org/show_bug.cgi?id=745443
As it's very common, handle driver not setting field in buffers
by using the field value from the format. This workaround a long time
bug in UVC driver. For even buggier driver, we simply assume
progressive as before. We also only warn once, to avoid spamming.
S_CROP ioctl is write-only and the device can adjust crop rectangle so
we query back the crop configuration after each S_CROP to know what has
been done.
https://bugzilla.gnome.org/show_bug.cgi?id=736133
In the V4L2 single-planar API, when format is semi-planar/planar,
drivers expect the planes to be contiguous in memory.
So this commit change the way we handle semi-planar/planar format
(n_planes > 1) when we use the single-planar API (group->n_mem == 1).
To check that planes are contiguous and have expected size, ie: no
padding. We test the fact that plane 'i' start address + plane 'i'
expected size equals to plane 'i + 1' start address. If not, we return
in error.
Math are done in bufferpool rather than in allocator because the
former is aware of video info.
https://bugzilla.gnome.org/show_bug.cgi?id=738013
Offset are relative to the buffer and there is no guarantee substracting
them will give us the plane size. So we let bufferpool make the math as
it is more aware of video info than allocator and pass a size array to
allocator import function.
Pointed out by Nicolas Dufresne <nicolas.dufresne@collabora.com>
https://bugzilla.gnome.org/show_bug.cgi?id=738013
Fixes stuttering audio when iOS AU is resampling. To make AU resample,
one has to request a rate that differs from AVAudioSession's
sampleRate. The resampling itself is not the culprit, but rather our
API misuse.
AudioUnitRender modifies the mDataByteSize members with the
actual read bytes count. Therefore, they must be reinitialized
before each AudioUnitRender. (The buffers themselves can be
preallocated.)
The "stutter" was caused by one AudioUnitRender making the buffer
too small for other AudioUnitRender invocations, making them fail
with -50 (paramErr). By way of luck, when AU didn't resample, all
AudioUnitRender invocations read the same number of bytes.
(This patch addresses some non-interleaved audio concerns, but
at this moment the elements do not support non-interleaved audio
and non-interleaved is untested.)
https://bugzilla.gnome.org/show_bug.cgi?id=744922
When there is no allocation parameters in the query, enable copy
threshold. When this threshold is reached, the buffer pool will start
copying when the pool reaches a critical level. If the driver supports
CREATE_BUFS, this will be used instead.
When we hit emulated formats, we disable CREATE_BUFS since libv4l2
cope very badly with it. Also clear the allocator flags so we will
never try to allocate more buffers. This fixes failure when the copy
threshold is reached as we where calling CREATE_BUFS, which lead to
libv4l2 instability.
In the fraction 1 / 2. 1 is the numerator and 2 is the denominator.
The arguments of fraction gst_value_set_fractions() are value,
numerator and denominator.
Also, gst_value_set_fraction() fails if denominator is 0 for obvious
reasons.
When importing buffers from a downstream pool, we need to deactivate
that pool to ensure it will be usable again later. Relying on the
refcount to reach zero does not work, since elements like xvimagesink
keeps a reference on their proposed pool.
When memory (that has been shared using gst_memory_share()) are freed,
the memory (or the DMABUF FD) should not bee freed. These memories have
a parent. This also removes the extra _v4l2mem_free function and avoid
calling close twice on the DMABUF FD.
https://bugzilla.gnome.org/show_bug.cgi?id=744573
Replace the sink_query with new getcaps() virtual and use the proxy
helper with the probed caps. This allow upstream element taking decision
base on what is supported downstream.
The hack causes deadlocks and other interesting problems and it really
can only be fixed properly inside GLib. We will include a patch for
GLib in our builds for now that handles this, and hopefully at some
point GLib will also merge a proper solution.
A proper solution would first require to refactor the polling in
GMainContext to only provide a single fd, e.g. via epoll/kqueue
or a thread like the one added by our patch. Then this single
fd could be retrieved from the GMainContext and directly integrated
into a NSRunLoop.
https://bugzilla.gnome.org/show_bug.cgi?id=741450https://bugzilla.gnome.org/show_bug.cgi?id=704374
v4l2loopback driver has a this nasty bug that if the queue is larger
then 2 buffers, it returns random index on dqbuf. So far we assumed
that the index was always right, which would lead to memory being
unref twice, and eventually crash.
As the buffer array is fixed size and small, it's safer to simply
use this static size to cleanup the buffers. This is also more
consistent with the rest. The associated method is no longer
required and can be dropped.
This partly revert to the old 1.2 behavior. Instead of keeping a
reference to the output buffer queued, we simply release them but
don't forward it to GstBufferPool. This way, the buffer pool don't
need to be flushed to be stopped.
https://bugzilla.gnome.org/show_bug.cgi?id=742074
Failing streamoff prevents allocator from being disposed hence
lead to device FD leak. There is no known cases where streamoff
may fails for which we'd still be streaming. streamoff is known
to fail when a device is being unplugged (in which case errno
19/ENODEV is set).
https://bugzilla.gnome.org/show_bug.cgi?id=732734
After creating the ringbuffer we have to set the device on the ringbuffer as
it defaults to kAudioDeviceUnknown. At this point it can't have changed to
anything else yet and we don't have to notify about changes to the sink/src
"device" property. It's also not a good idea because GstAudioBaseSrc has the
object lock taken while the ringbuffer is created, which might cause a
deadlock if something calls back into the element from "notify::device".
Once the base class is done with the NULL_TO_READY state change, it has opened
the device via the ringbuffer and this might have chosen a different device.
Especially if we initially used kAudioDeviceUnknown. Also notify about this
property change as initially intended by this code.
It looks like libv4l2 support for CREATE_BUF is incomplete. That
combine with existing bugs may lead to crash in GStreamer. These
check will make it robust by:
- Checking create buf index isn't an already in used index
- Checking that the index out of QUERYBUF matches the requested
index
Right now we try to be clever by detecting if device format have
changed or not, and skip setting format in this case. This is valid
behaviour with V4L2, but it's also very error prone. The rational
for not setting these all the time is for speed, though I can't
measure any noticeable gain on any HW I own. Also, until recently,
we where doing get/set on the format for each format we where
probing, making it near to impossible that the format would match.
This also fixes bug where we where skipping frame-rate setting if
format didn't change.
https://bugzilla.gnome.org/show_bug.cgi?id=740636
It's unlikely that setting a channel layout will do much for AC3/DTS
streams. If we find at some point that it does make sense, we can
perform the structure copying unconditionally (i.e., the current code is
wrong, since AC3/DTS will get two structures now - one with the channel
layout, one without).
https://bugzilla.gnome.org/show_bug.cgi?id=740987
Now that device selection has no sink/source-specific bits, we can have
generic device selection for this path. We do need to now track state
changes so we can look up the final device_id once the device is open,
though.
https://bugzilla.gnome.org/show_bug.cgi?id=740987
This is conceptually the right thing to do, and allows us to correctly
catch errors in device selection as well, which we could not do while
creating the ringbuffer.
https://bugzilla.gnome.org/show_bug.cgi?id=740987
If v4l2_buffer.field is V4L2_FIELD_INTERLACED, we set corresponding
GstVideoBuffer flags depending on the video standard.
According to V4L2 specification, M/NTSC transmits the bottom field
first, all other standards the top field first.
https://bugzilla.gnome.org/show_bug.cgi?id=737603
When libv4l2 emulates RW mode on top of MMAP devices, the queues are
only initialized on first read. The problem is that poll() will fail
if called before the queues are initialized and streaming. Workaround
this by doing a zero size read when pool is started in that IO mode.
https://bugzilla.gnome.org/show_bug.cgi?id=740633
This patch fixes CREATE_BUFS support for capture devices. Initially we
would only try and allocate more buffers when the copy threshold
is reached. When the threshold was not set (needed) it would never
happen. Another problem is that on capture side, acquire returns
filled buffer, hence need to pool. We need to set a special flag to
force allocation to happen.
https://bugzilla.gnome.org/show_bug.cgi?id=741134
This allow skipping buffer flagged with ERROR that has no payload.
This is typical behaviour when a recovererable error occured during
capture in the driver, but that no valid data was ever written into that
buffer. This patch also translate V4L2_BUF_FLAG_ERROR into
GST_BUFFER_FLAG_CORRUPTED. Hence decoding error produce
by decoder due to missing frames will now be correctly marked. Finally,
this fixes a buffer leak when EOS is reached.
https://bugzilla.gnome.org/show_bug.cgi?id=740040
If the v4l2 queue support dmabuf select this buffer pool mode
and update the query with allocator.
This patch only concern exporting dmabuf and not importing dmabuf
fd from downstream element.
https://bugzilla.gnome.org/show_bug.cgi?id=699382
Improve buffer validation by making sure each memory are the right
one and that each memory is writable. This fixes tearing issues in
case downstream uses gst_buffer_make_writable() or other type
of GstBuffer copy where memory are only reffed.
https://bugzilla.gnome.org/show_bug.cgi?id=739754
Rather than try and guess interlace support as part of checking supported
sizes, look for interlace support specifically in its own function.
As a cleanup, use V4L2_FIELD_ANY when probing sizes, which should result in
the driver doing the right thing.
With my capture setup, this gets me the following sample caps:
For 1080i resolution:
video/x-raw, format=(string)YUY2, width=(int)1920, height=(int)1080, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)interleaved, framerate=(fraction){ 25/1, 30/1 }
For 720p resolution:
video/x-raw, format=(string)YUY2, width=(int)1280, height=(int)720, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string)progressive, framerate=(fraction){ 50/1, 60/1 }
For 576i/p resolution (both possible at the point of query):
video/x-raw, format=(string)YUY2, width=(int)720, height=(int)576, pixel-aspect-ratio=(fraction)1/1, interlace-mode=(string){ progressive, interleaved }, framerate=(fraction){ 25/1, 50/1 }
This, in turn, makes 576i work correctly; with the old code,
the caps would be interlace-mode=progressive for interlaced video.
https://bugzilla.gnome.org/show_bug.cgi?id=726194
On streamon failure, the queued buffer is not released from the
bufferpool class point of view because it is queued to the driver and
the flush logic is not performed since we are not in streaming state.
It causes the v4l2 bufferpool to always return that stop method failed
and to leak v4l2 objects and buffers.
This commit solve this by performing the flush logic in error case, ie
flushing the allocator and restoring queued buffer state to non-queued.
https://bugzilla.gnome.org/show_bug.cgi?id=738102
This will prevent deadlocks, but will also properly flush the pool and allocator
when going to READY state. It should also fix issues reported on mailing list
when seeking is performed.
https://bugzilla.gnome.org/show_bug.cgi?id=738152
When the v4l2 device is an output device, the application shall set the
colorspace. So map GStreamer colorimetry info to V4L2 colorspace and set
on set_format. In case we have no colorimetry information, we try to
guess it according to pixel format and video size.
https://bugzilla.gnome.org/show_bug.cgi?id=737579
Use XQueryPointer to check that the pointer is actually active inside
the capturing region.
This prevents drawing the cursor when the pointer is partially outside
of the captured region but not active inside the region; in particular
this avoids drawing the "window resize" cursor shapes to the captured
image when the mouse pointer crosses a window border.
NOTE that this is not only an optimization, this also happen to fix
a serious problem in multi-screen setups.
Because XFixes gives no information of what screen the pointer is on,
ximagesrc was always drawing the cursor on the captured screen even if
the mouse pointer was on another screen.
For example, when capturing from screen 1 (i.e. display-name=":0.1") the
cursor was drawn in the captured image even when the mouse pointer was
actually on screen 0, which is wrong and visually confusing.
https://bugzilla.gnome.org/show_bug.cgi?id=690646
When the cursor is partially or totally out of the capturing region on
the top side or on the left side, it gets drawn fully inside of the
region with its coordinates rounded up to the left or to the top border.
This is immediately noticeable when using the xid property to capture
a specific window.
To fix the issue, allow negative cx and cx coordinates when checking the
boundaries before drawing the cursor.
NOTE that the boundaries checking calculations still allows the cursor
to be drawn when it is only partially outside of the capturing region,
but this makes sense and gives a more pleasing visual behaviour.
https://bugzilla.gnome.org/show_bug.cgi?id=690646
XFixes provides the cursor coordinates relative to the root window, this
is not taken into account when using the xid property to capture
a specific window, the result is that the cursor gets drawn at the wrong
position.
In order to fix this consider the window location when calculating the
cursor position in the destination image.
https://bugzilla.gnome.org/show_bug.cgi?id=690646
This will prevent the converter to be picked automatically in case
someone implement dynamic converter selection support. I'd like this
to be ranked only for known device, as it's hard to be sure a device is
a converter suited for general purpose. Re-negotiation is also needed
before we can rank it.
https://bugzilla.gnome.org/show_bug.cgi?id=733607
Even though the UVC driver do a great deal of effort to prevent bad
timestamp to be sent to userspace, there still exist UVC hardware that
are so buggy that the timestamp endup nearly random. This code detect
and ignore timestamp from these drivers, making these camera usable.
This has been tested on both invalid and valid cameras, making sure it
does not trigger for valid cameras.
https://bugzilla.gnome.org/show_bug.cgi?id=732910
There is still around 18 drivers not yet ported to videobuf2. These driver
don't support freeing buffetrs through REQBUFS(0) hence for these the
memory type probing fails. In order to gain back our previous behaviour in
presence of these, we implement a workaround that assuming MMAP is
supported. Note that an allocator is only created for device with
STREAMING support in the device capabilities. In such case one of MMAP,
USERPTR and DMABUF is required. Though DMABUF came afterward, so is
not an option and in practice none of these drivers will only do USERPTR.
https://bugzilla.gnome.org/show_bug.cgi?id=735660
Also-by: Hans de Goede <hdegoede@redhat.com>
Since we can get the minimum number of buffers needed by an output
device to work, use it to set min_latency which will determine how many
buffers are queued.
https://bugzilla.gnome.org/show_bug.cgi?id=736072
Most V4L2 ioctls like try_fmt will adjust input fields to match what the
hardware can do rather then returning -EINVAL. As is docmented here:
http://linuxtv.org/downloads/v4l-dvb-apis/vidioc-g-fmt.html
EINVAL is only returned if the buffer type field is invalid or not supported.
So upon requesting V4L2_FIELD_NONE devices which can only do interlaced
mode will change the field value to e.g. V4L2_FIELD_BOTTOM as only returning
half the lines is the closest they can do to progressive modes.
In essence this means that we've failed to get a (usable) progessive mode
and should fall back to interlaced mode.
This commit adds a check for having gotten a usable field value after the first
try_fmt, to force fallback to interlaced mode even if the try_fmt succeeded,
thereby fixing get_nearest_size failing on these devices.
https://bugzilla.gnome.org/show_bug.cgi?id=735660
They may have been modified by the ioctl even if it failed. This also makes
the S_FMT fallback path try progressive first, making it consistent with the
preferred TRY_FMT path.
https://bugzilla.gnome.org/show_bug.cgi?id=735660
If the minimum required buffer exceed V4L2 capacity, don't share down
pool. This allow support very high latency, like with x264enc default
encoding settings.
https://bugzilla.gnome.org/show_bug.cgi?id=732288
Some v4l2 devices could require a minimum buffers different from default
values. Rather than blindly propose a pool with min-buffers set to the
default value, it ask the device using control ioctl.
https://bugzilla.gnome.org/show_bug.cgi?id=733750
