Also add a FIXME in gst_v4l2_object_setup_format
to note that the whole function has to be improved
in order to support ENCODED formats.
It requires to have an encoder device which we do not
have right now.
https://bugzilla.gnome.org/show_bug.cgi?id=720568
This method allow setting up the object from the currently configured format on the
device. This is useful for M2M element where input data decides the format that will
be set on capture side.
https://bugzilla.gnome.org/show_bug.cgi?id=720568
The number of plane, and the stride does not represent a capability change. Same caps
can have different stride from the default GstVideoInfo and the number of planes will
never change for 1 format.
https://bugzilla.gnome.org/show_bug.cgi?id=720568
It makes the gst_v4l2_object_set_format() slightly simplier and will make that
logic reusable. Note that gst_v4l2_object_has_mplane() will always return the
same value for one device. There is no need to check against the caps as this
has already been done by _open.
https://bugzilla.gnome.org/show_bug.cgi?id=720568
We set the dimensions just in case but don't validate them
afterwards. For some codecs the dimensions are *not* in the
bitstream, IIRC VC1 in ASF mode for example.
https://bugzilla.gnome.org/show_bug.cgi?id=720568
so that the buffer informations can be retrieved the same way
in both MPLANE and non-MPLANE mode.
Here "emulating" means "manually fill in the plane".
Fixes bug https://bugzilla.gnome.org/show_bug.cgi?id=712754
This api is in linux kernel since version 2.6.39,
and present in all version 3.
The commit that adds the API in master branch of the
linux kernel source is:
f8f3914cf9
v4l2 doc: "Some devices require data for each input
or output video frame to be placed in discontiguous
memory buffers"
There are newer structures 'struct v4l2_pix_format_mplane'
and 'struct v4l2_plane'.
So the pixel format is not setup with the same API when using
multi-planar.
Also for gst-v4l2, one of the difference is that in GstV4l2Meta
there are now one mem pointer for each maped plane.
When not using multi-planar, this commit takes care of keeping
the same code path than previously. So that the 2 cases are
in two different blocks triggered from V4L2_TYPE_IS_MULTIPLANAR.
Fixes bug https://bugzilla.gnome.org/show_bug.cgi?id=712754
It's unfortunate to have to do this, but with the mix of tabs and space, plus all the random
indentation this header has become very hard to read.
https://bugzilla.gnome.org/show_bug.cgi?id=712754
On some systems (E.G. uClibc and older Glibc versions), O_CLOEXEC is only
defined when _GNU_SOURCE is specified, so do so.
_GNU_SOURCE needs to be defined before any system headers are included,
so move the fcntl.h section up.
https://bugzilla.gnome.org/show_bug.cgi?id=709423
If the pool is stopped while gst_v4l2_buffer_pool_dqbuf() waits for a
buffer then the return value is GST_FLOW_FLUSHING. In this case the buffer
to queue must also be released. Otherwise is will never be deleted or
returned to its pool.
https://bugzilla.gnome.org/show_bug.cgi?id=703764
gst_video_info_from_caps() always extract width, height, interlace mode and
framerate now. It is no longer necessary to do it again for encoded
formats.
https://bugzilla.gnome.org/show_bug.cgi?id=703399
As cameras tend to have a quite specific set of capabilities (specific
framerates for each resolution), getting the peer caps filtered by our
probed caps can cause a big increase in the caps size which slows down
things quire a bit.
As for negotiation v4l2 iterates through the caps of the peer to find the
first intersection with the probed caps, getting the fully expanded
intersection of capabilities is not useful.
Using the same testcase as for bug #702632, adding this patch on top of
the patches suggested there speeds up getting the inital frame from
around ~14-15 seconds to around ~3-4 seconds.
https://bugzilla.gnome.org/show_bug.cgi?id=702638
The pool accesses data from the v4l2object so it must exist at least
as long as the pool. Refcount the element which controls the object
live-time.
https://bugzilla.gnome.org/show_bug.cgi?id=701650
In v2.6.18 control classes where added to the v4l2 API.
Iterating over CIDs starting with V4L2_CID_BASE will only find controls for
the first control class.
By iterating with V4L2_CTRL_FLAG_NEXT_CTRL all controls are found.
This is necessary to make controls from other control classes available in
the extra-controls property.
If V4L2_CTRL_FLAG_NEXT_CTRL is not defined at compile time or not supported
at runtime then the old mechanism for iterating is used.
https://bugzilla.gnome.org/show_bug.cgi?id=701540
Instead of just assuming a aspect ratio of 1/1 use VIDIOC_CROPCAP to ask
the device.
This also add a pixel-aspect-ratio property to overwrite the value from the
driver and a force-aspect-ratio property to ignore it.
https://bugzilla.gnome.org/show_bug.cgi?id=700285
Without this the following sequence fails:
- set_caps()
- object_stop() (does nothing)
- set_format() -> VIDIOC_S_FMT
- set_config() -> VIDIOC_REQBUFS with count = N
- set_caps()
- object_stop()
- pool_finalize()
- set_format() -> VIDIOC_S_FMT => EBUSY
Usually the pool is started after set_config(), in which case object_stop()
will result in a pool_stop and therefore VIDIOC_REQBUFS with count = 0 but
that is not guaranteed.
Also calling VIDIOC_REQBUFS with count = 0 in pool_finalize() if necessary
fixes this problem.
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=701543
This is a followup patch for #700781, which is not quite correct.
The buffer handling is quite complicated here.
The original code intended to the the following:
- gst_v4l2_buffer_pool_process() calls QBUF and adds the buffer to the
local list.
- The sink calls gst_buffer_unref() which returns the buffer to the pool
but not the 'free list'.
- Some time later DQBUF returns the buffer and
gst_v4l2_buffer_pool_release_buffer() puts in on the 'free list'.
If the buffer must be copied then (parent_class)->acquire_buffer() is
called directly to keep the buffer in the pool.
This has two problems:
1. If gst_v4l2_buffer_pool_release_buffer() is called before the buffer is
returned to the pool, then the buffer is put on the 'free list' twice.
This can happen if a reference to the buffer is kept outside the sink,
of if DQBUF returns the buffer, that was just queued with QBUF.
2. If buffers are copied, then all buffers are in the pool at all times. As
a result gst_v4l2_buffer_pool_stop() and gst_v4l2_buffer_pool_dqbuf()
can access pool->buffers at the same time, which can lead to memory
corruption.
The patch for #700781 fixes those problems, but with the side effect that
there are always buffers outside the pool (because they are queued) and
the pool is never stopped.
This patch fixes this by releasing the reference to the buffer after
handling it (to avoid problem 2.) so it can be returned to the pool.
gst_v4l2_buffer_pool_release_buffer() is only called if the buffer is
already in the pool (to avoid problem 1.).
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=701375
This makes it possible to set any controls that can be set with
VIDIOC_S_CTRL.
The controls are set when the property is set (if the device is open)
and when the device is opened.
https://bugzilla.gnome.org/show_bug.cgi?id=698837
Without this, a queued buffer may be required, filled and queued before it
is dequeued.
Calling gst_buffer_pool_acquire_buffer() ensures that the buffer is set up
correctly and gst_buffer_unref() calls buffer_release().
https://bugzilla.gnome.org/show_bug.cgi?id=700781
This can happen if other parts of the pipeline are reconfigured.
Stop streaming even for a short amount of time can be quite visible, so it
should be avoided if possible.
https://bugzilla.gnome.org/show_bug.cgi?id=700503
When queuing a buffer for a sink, bytesused must contain the actual
amount of data.
For a source, the driver must overwrite this, so it doesn't matter
what is set here.
https://bugzilla.gnome.org/show_bug.cgi?id=699598
In the past gst_video_info_from_caps() only video/x-raw. Now it also
supports other video/* and image/* formats.
With this patch the format won't be GST_VIDEO_FORMAT_UNKOWN and
gst_v4l2_buffer_pool_set_config() handles strides correctly.
https://bugzilla.gnome.org/show_bug.cgi?id=699570
If max_buffers is 0 then an arbitrary number of buffers (currently 4) is
allocated. If this is not enough v4l2src starts copying buffers.
With this patch VIDIOC_CREATE_BUFS is used to allocate a new buffer. If
this fails v4l2src falls back to copying buffers.
https://bugzilla.gnome.org/show_bug.cgi?id=699447
The existence of a GstVideoFormatInfo does not guarantee, that
the buffer contains video frames, so the format must be checked.
Also, for encoded buffers the length is variable and must be set.
https://bugzilla.gnome.org/show_bug.cgi?id=698949
If TRY_FMT is not implemented, gst_v4l2_object_get_nearest_size will
use S_FMT and will change the device's operation mode. To save the
old device mode we need to set the type field or else it will fail
to save the previous format.
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=685209
Don't just loop over the first num_queued buffers but loop over
all the buffers and check if they need to be freed. It is possible that
not all buffers are queued and then the entry in our array will be NULL.
Those buffers that are not queued were freed in stop().
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=696651
v4l has add a new IOCTL to export a buffer by using dmabuf.
This patch allow to use this new IOTCL if it has been defined in videodev2.h
I introduce a new IO mode (GST_V4L2_IO_DMABUF) to enable this way of working.
https://bugzilla.gnome.org/show_bug.cgi?id=693826
With the port to gstreamer 1.0 the prepare-format signal stopped being
emitted. Start emitting this again for use in uvch264src. While there
change the emission to include the caps for extra flexibility instead of
fource, width, height.
https://bugzilla.gnome.org/show_bug.cgi?id=692042
Need to explicitly link against -lrt for clock_gettime(), which
we don't get in the libs any more, because core moved the
gmodule-no-export-2.0 bit into Requires.Private.
Not required for newer glibc, but for older ones, so check for that.
When do v4l2_ioctl() with VIDIOC_ENUMINPUT fails on some devices,
kernels before 3.3.0 return EINVAL, but newer kernels return ENOTTY.
This patch make those devices work well on kernel 3.3+.
Related kernel commit:
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commit;h=07d106d0a33d6063d2061305903deb02489eba20
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Rui Wang <wangr@lemote.com>
Signed-off-by: Jie Chen <chenj@lemote.com>
This was unused apparently and removed in the kernel in commit:
From 2b719d7baf490e24ce7d817c6337b7c87fda84c1 Mon Sep 17 00:00:00 2001
From: Sakari Ailus <sakari.ailus@iki.fi>
Date: Wed, 2 May 2012 09:40:03 -0300
Subject: [PATCH] [media] v4l: drop v4l2_buffer.input and V4L2_BUF_FLAG_INPUT
Remove input field in struct v4l2_buffer and flag V4L2_BUF_FLAG_INPUT which
tells the former is valid. The flag is used by no driver currently.
https://bugzilla.gnome.org/show_bug.cgi?id=681491
Conflicts:
sys/v4l2/gstv4l2bufferpool.c
UVC devices are never interlaced, and doing VIDIOC_TRY_FMT on them
causes expensive and slow USB IO, so don't probe them for interlaced.
This shaves 2 seconds of the startup time of cheese with a Logitech
Webcam Pro 9000.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Fixes https://bugzilla.gnome.org/show_bug.cgi?id=677722
input.std is of type v4l2_std_id which is defined as 64-bit unsigned integer.
Casting to uint means the higher bits, wich are used for the private video
standards of the TI video capture/display driver for example, are lost.
Sample the pipeline clock and device clock closer to eachother to reduce jitter.
Don't subtract the frame duration from the timestamp when we can use the device
timestamps.
Assume a delay of 1 frame in read-write mode.
Query the amount of available buffers when doing set_config(). This allows us to
configure the parent bufferpool with the number of buffers to preallocate.
Keep track of the provided allocator and use it when we need to allocate a
buffer in RW mode.
When we are can not allocate the requested max_buffers amount of buffers, make
sure we keep 2 buffers around in the pool and copy them into an output buffer.
This makes sure that we always have a buffer to capture into. We also need to
detect those copied buffers and unref them when they return to the pool.
Only free the queued buffers that we keep track of in our buffer array. for rw
io-mode, we do allocate buffers but we don't keep track of them in the buffer
array.
This is not enough to properly support H264 cameras, but it will
allow an H264 stream to be generated by v4l2src using the default
settings of the camera. If used with the pre-set-format signal, the
H264 encoder can be fully configured.
Conflicts:
sys/v4l2/gstv4l2object.c
In order to support UVC H264 encoding cameras, an H264 Probe&Commit
must happen before the normal v4l2 set-format. This new signal is
meant to allow an external application or bin to do it.
It also serves to expose the file descriptor used by v4l2src in case
some custom ioctls need to be called.
Conflicts:
sys/v4l2/Makefile.am
sys/v4l2/gstv4l2src.c
sys/v4l2/v4l2src_calls.c
The tuner marshal and enumtypes are autogenerated, and they need
to be created before the compilation of gstv4l2tuner.c
This patch adds the automake instruction for ensuring the
autogeneration of those files previous the compilation.
The base class may have set the DISCONT flag on the first buffer pushed
out. We need to clear that when recycling buffers back into the buffer
pool, otherwise we constantly push out buffers with the discont flag
set, which might upset downstream elements, esp. for compressed
formats like mpeg-ts.
Make sure we always call munmap() with the same size we called mmap()
with before.
Current v4l2src uses the same structure for VIDIOC_QUERYBUF, VIDIOC_QBUF
and v4l2_munmap calls. The problem is that the video buffer size (length)
may vary for compressed or emulated bufs. VIDIOC_QBUF will change it if
we pass the pointer of a v4l2_buffer. This is why we should avoid using
same variable for mmap and video buffers.
https://bugzilla.gnome.org/show_bug.cgi?id=671126
Don't post a (fatal) error message on the bus just because we
failed to query some control. Fixes issue with built-in
Suyin Corp webcam for HP notebook (usbid 064e:e28a) on
OpenSuse 12.1, where querying red/blue balance fails.
https://bugzilla.gnome.org/show_bug.cgi?id=670197
Add private replacements for deprecated functions such as
g_mutex_new(), g_mutex_free(), g_cond_new() etc., mostly
to avoid the deprecation warnings. We'll change these
over to the new API once we depend on glib >= 2.32.
We don't currently support setting the pixel-aspect-ratio from V4L2. So
simply set it to be 1/1 in the caps to prevent negotiation failures when
fixating to weird values (e.g. when the downstream caps has
pixel-aspect-ratio = [ MIN, MAX ] )
https://bugzilla.gnome.org/show_bug.cgi?id=663580
We used to skip frame rate setup if the camera was already setup
with the requested frame rate. This breaks some cameras though,
causing them to not output data (several models of Thinkpad cameras
have this problem at least).
So, don't skip.
https://bugzilla.gnome.org/show_bug.cgi?id=638300
Some drivers are buggy are will change the current format when
processing VIDIOC_TRY_FMT. Save and restore the current format
to ensure the format is kept unchanged.
https://bugzilla.gnome.org/show_bug.cgi?id=649067
Use the fraction compare utility to compare function, not the
handcrafted one. The handcrafted one is buggy as it doesn't take into
account rounding error. For example comparing a framerate of 20/1 on a
camera configured as 30/1 fps would yield true: 1 == (1 * 20)/30 and not
re-configure the camera. Fixes#656104
When nobody is using our pool, activate it ourselves.
Avoid leaking the buffer array.
Set default pool configuration with caps.
Don't keep current_caps, core does that for us now.
Use the more specialized type for the bufferpool.
Use the size from the driver as the size of the image to read.
Don't configure the pool when created. This will be done in the setup_allocation
method later or by upstream for sinks.
Remove unused properties and variables. Bufferpool sizes are now configured in
the bufferpool by the elements in the pipeline. We might want to influence the
pool size later somehow.
Prefer to always use the default bufferpool queue for the _acquire function
because it properly supports unblocking when setting inactive etc. As a result,
we need to dequeue buffers and put them back in the bufferpool queue when we
have queued all buffers in the sink.
Rename some variables to more meaningfull names to avoid a problem with
freeing the wrong amount of buffers.
Remove old method, use neww _process method for the sink.
Inform the parent bufferpool class about the settings too. This is needed to let
it know about the max-buffers.
Allocate the negotiated max-buffers and initially mmap min-buffers. The idea is
that the bufferpool will allocate more when needed.
Improve debugging.
Only poll in capture mode, it does not seem to work in playback mode on this
beagleboard.
Add different transport methods to the bufferpool (MMAP and READ/WRITE)
Do more parsing of the bufferpool config.
Start and stop streaming based on the bufferpool state.
Make separate methods for getting a buffer from the pool and filling it with
data. This allows us to fill buffers from other pools too. Either use copy or
read to fill up the target buffers.
Add property to force a transfer mode in v4l2src.
Increase default number of buffers to 4.
Negotiate bufferpool and its properties in v4l2src.
Pass the caps and the default video size to the bufferpool config.
Don't activate the bufferpool, this will be done by the object that decides to
use the bufferpool.
Improve debugging and error reporting.
When we have all buffers queued for playback and we need a new empty buffer,
dequeue one and return it.
Set the right size for sink buffers.
Improve counting of queued buffers.
Extend from GstBufferPool.
Handle the lifetime of the pool buffers correctly with the start/stop vmethods.
Map acquire and release directly to QBUF and DQBUF. We still expose an explicit
qbuf for the v4l2sink for now.
Move the details of how to capture to the device object. Remove the
v4l2src_calls.[ch] files because they are empty now.
Provide two simple methods to get and return a buffer to the device.
Also do a slow copy when the buffer is not from our pool.
Rename start and stop methods to open and close because that is what they do.
After setting the format on the device object, setup the bufferpools. Move this
code from the v4l2src_calls.c file, it is shared between source and sink.
Make new device start and stop method that merges various bits of common code
spread over several files.
We want to keep the default strides in the videoinfo. Keep the stride of the
video frames separate so that we can use both to copy a video frame and do
correct stride conversion.
Use GstVideoInfo to store the parsed caps.
Remove outsize from the caps parsing code, it's wrong because it does not use
the stride given by the driver.
Move the configuration of the framerate to where we set the other format
parameters.
Remove hack to check if the device is active.
Store streamparm in the device info.
Use some macros to access the current device configuration.
Remove some duplicate fields in src and sink and use the device configuration
instead.
Pass the caps to the set_format function and make _set_format parse the caps.
Also keep the parsed values in the v4l2object so that we can refer to them when
we want.
Keep track of the currently configured format and setting in the
v4l2object.
Pass the v4l2object to the bufferpool constructor so that the bufferpool can
know everything about the currently configured settings. This also allows us
to remove some awkward code.
Create a new pool in setcaps and stop/destroy the old one.
Remove buffer_alloc functions.
Check that we have v4l2 metadata in show_frame and fall back to memcpy into a
buffer from our pool if we don't receive one of our own buffers.
Various cleanups, avoids useless casts, move error handling outside of the main
code flow.
Negotiate to a resonable resolution instead of the max resolution.
Based on a patch by Guennadi Liakhovetski.
v2: updates because I forgot to add GstTuner interface to v4l2sink
v3: update to add all possible values to norm enum
Commit 6c8268dbfd broke recording
from interlaced v4l2 source (e.g. typical tv capture card) since
V4L2_FIELD_SEQ_TB (with fields stored separately) does not map
to currently defined interlaced format (fields stored interleaved).
Besides this mismatch, hardware might quite likely not support or
appreciate this field value, since querying supported formats mapped
_INTERLACED field formats to interlaced=true caps (so the latter should
not be mapped to field value that is not known to be supported).
Older kernels don't have these, and there's no easy way to check for the
existance of enums that doesn't involve a configure check, so just define
these if the V4L2_CAP_VIDEO_OUTPUT_OVERLAY define is not there, which was
added in the same commit as the TB/BT enum. Fixes compilation on CentOS 5.
https://bugzilla.gnome.org/show_bug.cgi?id=639339
These macros will expand to NOOPs given the right defines. Also,
g_return_if_fail() and friends are meant to be used to catch programming
errors (like invalid input to functions), not runtime error handling.
Looks like this got enabled by accident when adding it to v4l2sink,
so undo this for now. Not sure it makes much sense in a GStreamer
context with current hardware.
This reverts commit 9e1d419d07.
Reverting this since it adds unreviewed and bad API to v4l2src
(property of type enum, with seemingly random and unsorted values).
output devices should use get/set output, and in either case we should
not print a warning message if the ioctl fails but the device does not
claim to support the tuner interface
If xoverlay is available, v4l2sink should create a window for the overlay to
display in.
The window automatically tries to make itself as large as possible.
This works well on a small screen, but perhaps should first attempt to use
the size of the video that is played (no scaling).
Special case check for sub-buffers: In certain cases, places like
GstBaseTransform, which might check that the buffer is writable before copying
metadata, timestamp, and such, will find that the buffer has more than one
reference to it. In these cases, they will create a sub-buffer with an offset=0
and length equal to the original buffer size.
This could happen in two scenarios: (1) a tee in the pipeline, and (2) because
the refcnt is incremented in gst_mini_object_free() before the finalize function
is called, and decremented after it returns.. but returning this buffer to the
buffer pool in the finalize function, could wake up a thread blocked in
_buffer_alloc() which could run and get a buffer w/ refcnt==2 before the thread
originally unref'ing the buffer returns from finalize function and decrements
the refcnt back to 1!
This is related to issue #545501
The size of the buffer would be zero'd out in gst_v4l2_buffer_finalize()
after the buffer is qbuf'd or pushed onto the queue of available buffers..
leaving a race condition where the thread waiting for the buffer could awake
and set back a valid size before the finalizing thread zeros out the length.
This would result that the newly allocated buffer has length of zero.
When v4l2sink goes to PAUSED->READY it only stops streaming, so the state
should be set to STATE_PENDING_STREAMON in case the element transitions
back to PLAYING.
We'd prefer to throttle the decoder if we run out of buffers, to keep a bound
on memory usage. Also, for OMAP4 it is a requirement of the decoder to not
alternate between memory alloced by the display driver and malloc'd userspace
memory.
note: this really only affects v4l2sink since gst_v4l2_buffer_pool_get() is
only called once per buffer in the v4l2src case (in
gst_v4l2src_buffer_pool_activate())
Most v4l2 drivers will get upset when you queue the same buffer twice in a
row without first dequeueing it.
Rendering of pre-roll buffers can be re-introduced later, but will require
tracking the state of the buffer, and avoiding to re-QBUF if the buffer has
already been passed to the driver.
When the decoder is using pad_alloc(), v4l2sink would behave badly if
the number of buffers ('queue-size' property) was not high enough to
account for all the buffers needed by the decoder, and other elements
(such as queues) between the decoder and v4l2sink. This patch
slightly increases the default number of buffers, and changes v4l2sink
to drop frames rather than return an error in case the number of
buffers is not high enough.
with i686-apple-darwin10-gcc-4.2.1:
gstv4l2object.c: In function 'gst_v4l2_object_get_nearest_size':
gstv4l2object.c:1988: warning: format '%u' expects type 'unsigned int', but argument 12 has type 'gint *'
gstv4l2object.c:1988: warning: format '%u' expects type 'unsigned int', but argument 13 has type 'gint *'
it's perfectly ok for a video output device to not have overlay capabilities.
this patch removes the need to get/set the overlay parameters if the user
does not explicitely request one of the overlay properties
MPEG doesn't have a static size per frame, so don't pretend it has one
and fail when capturing because it doesn't match. Instead mark the size
as unknown and let the read frame grabbing method use a reasonable fallback
value (assuming that's only for actual streaming formats)
Fixes bug #628349.
The format list should be sorted from high ranks to low ranks. In the GSList
sorting function this means the compare needs to return a positive value if
format a has a lower rank than format b.
Among other things this fixes v4l2src to prefer non-emulated formats
to emulated formats when built against libv4l.
In the case we change the State from READY_TO_NULL the buffers in the pool
still hold an open dup file descriptor to the device, therefore the device
release function will not be called and the device will probably answer with
-EBUSY when we reopen it in the next NULL_TO_READY transition.
Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
See bug #622500 and #612244.
This allows set_caps to succeed if caps change in a way that
would not modify the format we're getting from the hardware.
Otherwise if not in NULL state, setting caps would fail
with EBUSY.
With this change, in some cases it's OK to go PLAYING->READY->PLAYING
rather than PLAYING->NULL->PLAYING to avoid a time-consuming close
and reopen of the device.
Fixes#621723
Fixes#621723 (partially)
set_caps can fail if the video device is running, in that case
setting its format leads to EBUSY.
If set_caps fails then we will not have set up the buffer pool
(it will be NULL) which leads to a crash when we try to pull
buffers. If we fail the negotiate on set_caps failure, then we
won't go to playing state and won't crash.
This is a small improvement. Of course, a nicer fix would
be to make set_caps work in the case where the format is
unchanged. If the format has changed, failing is
probably correct because we need to close the device
(go to NULL state) in order to set caps.
