Fall back on PATH_DEV_DSP if nothing is set.
This mirrors the behaviour of --audio-device / --alsa-device.
There doesn't appear to be a general way to list devices with oss, so
--audio-device=help doesn't list oss devices except for the default one if the
file exists.
Previously --audio-device was ignored entirely by ao_oss.
fixes#4122
See: https://msdn.microsoft.com/en-us/library/windows/desktop/dd743946.aspx
Microsoft example code often uses a SAFE_RELEASE macro like the one in
the above link. This makes it easier to avoid errors when releasing COM
interfaces. It also reduces noise in COM-heavy code.
ao_wasapi.h also had a macro called SAFE_RELEASE, though unlike the
version above, its SAFE_RELEASE macro accepted a second parameter which
allowed it to destroy arbitrary objects other than just COM interfaces.
This renames ao_wasapi's SAFE_RELEASE to SAFE_DESTROY, which should more
accurately reflect what it does and prevent confusion with the Microsoft
version.
We log a large number of formats, but we rarely log the result of the
probing. Change this.
The logic in try_format_exclusive() changes slightly, but should be
equivalent. EXIT_ON_ERROR() checks for FAILED(), which should be
exclusive to SUCCEEDED().
Long planned. Leads to some sanity.
There still are some rather gross things. Especially g_groups is ugly,
and a hack that can hopefully be removed. (There is a plan for it, but
whether it's implemented depends on how much energy is left.)
Until now, this was only implemented for ao_alsa and AOs not using
push.c. ao_alsa.c relied on enabling funny underrun semantics for
avoiding resets on lower levels, while other AOs using push.c didn't do
anything.
Change this and at least make push.c copy silent data to the AO. This
still isn't perfect as keeping track of how much silence was played when
seems complex, so we don't do it. The consequence is that frame-stepping
will essentially randomize the A/V offset (it'll recover immediately
when unpausing, but still ugly). Also, in order to empty the currently
buffered audio on seeks etc., we still call ao_driver->reset and so on,
so the AO driver will still need to handle this specially.
The intent is to make behavior with ALSA less weird (for one we can
remove the code in ao_alsa.c that tries to trigger an initial
underflow). Also might help with #3754.
The "default" entry (which is and always was mpv/mplayer's default) does
not have a description set in the ALSA API. (While "sysdefault"
strangely has.)
Instead of an empty description, this should show something nice, so
reuse the ao.c code for naming default devices (see previous commit).
It's still a bit ugly that audio-device-list will have a default entry
for "Autoselect device" and "Default (alsa)", but then again we probably
want to allow the user to force ALSA (i.e. prevent fallbacks to other
AOs) just because ALSA is so flaky and makes this a legitimate feature.
This will make it easier for AOs to add explicit default device entries.
(See next commit.)
Hopefully this change doesn't lead accidentally to bogus "Default"
entries to appear, but then it can only happen if the device ID is
empty, which would mean the underlying audio API returned bogus entries.
Use the device name as fallback. This is ugly, but still better than
skipping the description entirely. This can be an issue on ALSA, where
the API can return entries without proper description.
This happens when ALSA gives us more channels than we asked for, for
whatever reasons. It looks like this wasn't handled correctly. The mpv
and ALSA channel counts could mismatch, which would lead to UB.
I couldn't actually trigger this case, though. I'm fairly sure that
drivers or plugins exist that do it anyway. (Inofficial ALSA motto: if
it can be broken, then why not break it?)
If the input is already mono or stereo, or if channel map selection
results in mono or stereo, then disable further use of the champ ALSA
API (or rather, stop trusting its results). Then we behave like a simple
application that only wants to output mono or stereo.
See #3045 and #2905. I couldn't actually test these cases, but this
commit is supposed to fix them.
set_chmap() skipped _setting_ the ALSA chmap if chmap use was requested
to be disabled by setting dev_chmap.num=0 by the caller, but it still
queried the current ALSA channel map. We don't trust it that much, so
disable that as well.
But we still query and log it, because that could be helpful for
debugging. Otherwise we could skip the entire set_chmap() call in these
cases.
If the "default" device refuses to be opened as spdif device (i.e. it
errors due to the AES0 etc. parameters), we were falling back to the
iec958 device. This is needed on some systems for smooth operation with
PCM vs. spdif.
Now change it to try "hdmi" before "iec958", which supposedly helps in
other situations.
Better suggestions welcome. Apparently kodi does this too, although I
didn't check directly.
The player tries to avoid splitting frames with spdif (sample alignment
stuff). This can in certain corner cases with certain drivers lead to
the situation that ao_get_space() returns a number higher than 0 and
lower than the audio frame size. The playloop will round this down to 0
bytes and do nothing, leading to a missed wakeup. This can lead to
underruns or playback completely getting stuck.
It can be reproduced by playing AC3 passthrough with no video and:
--ao=null --ao-null-buffer=0.256 --ao-null-outburst=6100
This commit attempts to fix it by allowing the playloop to write some
additional data (to get a complete frame), that will be buffered within
the AO ringbuffer even if the audio device doesn't want it.
We always want to use __declspec(selectany) to declare GUIDs, but
manually including <initguid.h> in every file that used GUIDs was
error-prone. Since all <initguid.h> does is define INITGUID and include
<guiddef.h>, we can remove all references to <initguid.h> and just
compile with -DINITGUID to get the same effect.
Also, this partially reverts 622bcb0 by re-adding libuuid.a to the
build, since apparently some GUIDs (such as GUID_NULL) are not declared
in the source file, even when INITGUID is set.
There were multiple values under M_OPT_EXIT (M_OPT_EXIT-n for n>=0).
Somehow M_OPT_EXIT-n either meant error code n (with n==0 no error?), or
the number of option valus consumed (0 or 1). The latter is MPlayer
legacy, which left it to the option type parsers to determine whether an
option took a value or not. All of this was changed in mpv, by requiring
the user to use explicit syntax ("--opt=val" instead of "-opt val").
In any case, the n value wasn't even used (anymore), so rip this all
out. Now M_OPT_EXIT-1 doesn't mean anything, and could be used by a new
error code.
Currently, calling mp_input_wakeup() will wake up the core thread (also
called the playloop). This seems odd, but currently the core indeed
calls mp_input_wait() when it has nothing more to do. It's done this way
because MPlayer used input_ctx as central "mainloop".
This is probably going to change. Remove direct calls to this function,
and replace it with mp_wakeup_core() calls. ao and vo are changed to use
opaque callbacks and not use input_ctx for this purpose. Other code
already uses opaque callbacks, or has legitimate reasons to use
input_ctx directly (such as sending actual user input).
The first one is printed even if the user disabled video (or there's no
video), so just remove it. The second one uses deprecated sub-option
syntax, so remove that as well.
And introduce a global option which does this. Or more precisely, this
deprecates the global wasapi and coreaudio options, and adds a new one
that merges their functionality. (Due to the way the sub-option
deprecation mechanism works, this is simpler.)
I decided that it's too much work to convert all the VO/AOs to the new
option system manually at once. So here's a shitty hack instead, which
achieves almost the same thing. (The only user-visible difference is
that e.g. --vo=name:help will list the sub-options normally, instead of
showing them as deprecation placeholders. Also, the sub-option parser
will verify each option normally, instead of deferring to the global
option parser.)
Another advantage is that once we drop the deprecated options,
converting the remaining things will be easier, because we obviously
don't need to add the compatibility hacks.
Using this mechanism is separate in the next commit to keep the diff
noise down.
Instead of requiring each VO or AO to manually add members to MPOpts and
the global option table, make it possible to register them automatically
via vo_driver/ao_driver.global_opts members. This avoids modifying
options.c/options.h every time, including having to duplicate the exact
ifdeffery used to enable a driver.
Normally I'd prefer a bunch of smaller functions with fewer parameters
over a single function with a lot of parameters. But future changes will
require messing with the parameters in a slightly more complex way, so a
combined function will be needed anyway. The now-unused "global"
parameter is required for later as well.
Positional parameters cause problems because they can be ambiguous with
flag options. If a flag option is removed or turned into a non-flag
option, it'll usually be interpreted as value for the first sub-option
(as positional parameter), resulting in very confusing error messages.
This changes it into a simple "option not found" error.
I don't expect that anyone really used positional parameters with --vo
or --ao. Although the docs for --ao=pulse seem to encourage positional
parameters for the host/sink options, which means it could possibly
annoy some PulseAudio users.
--vf and --af are still mostly used with positional parameters, so this
must be a configurable option in the option parser.
With the previous commit, ao_alsa.c now has 3 possible ways to pause
playback. Actually all 3 of them need get_delay() to fake its return
value, so don't duplicate that code.
Also much of the code looks a bit questionable when considering
inconsistent pause/resume calls from outside, so ignore redundant calls.
push.c does not handle this automatically, and AOs using push.c have to
handle it themselves. Also, ALSA is low-level enough that it needs
explicit support in user code. At least I haven't found any option that
does this.
We still can get away relatively cheaply by abusing underflow-handling
for this. ao_alsa.c already configures ALSA to handle underflows by
playing silence. So we purposely induce an underflow when opening the
device, as well as when pausing or resetting the device.
This introduces minor misbehavior: it doesn't account for the additional
delay the initial silence adds, unless the device has fully played the
fragment of silence when the player starts sending data to it. But
nobody cares.
Exactly the same situation as with ao_alsa in commit 0b144eac (except
that we can detect the situation better under wasapi).
Essentially, wasapi will allow us to output any sample format, and not
just the one configured by the user in the audio system settings.
This commit adds an --audio-channel=auto-safe mode, and makes it the
default. This mode behaves like "auto" with most AOs, except with
ao_alsa. The intention is to allow multichannel output by default on
sane APIs. ALSA is not sane as in it's so low level that it will e.g.
configure any layout over HDMI, even if the connected A/V receiver does
not support it. The HDMI fuckup is of course not ALSA's fault, but other
audio APIs normally isolate applications from dealing with this and
require the user to globally configure the correct output layout.
This will help with other AOs too. ao_lavc (encoding) is changed to the
new semantics as well, because it used to force stereo (perhaps because
encoding mode is supposed to produce safe files for crap devices?).
Exclusive mode output on Windows might need to be adjusted accordingly,
as it grants the same kind of low level access as ALSA (requires more
research).
In addition to the things mentioned above, the --audio-channels option
is extended to accept a set of channel layouts. This is supposed to be
the correct way to configure mpv ALSA multichannel output. You need to
put a list of channel layouts that your A/V receiver supports.
When selecting a device that simply doesn't exist with --audio-device,
AudioUnit will still initialize and start playback without complaining.
But it will never call the audio render callback, which leads to audio
playback simply not progressing.
I couldn't find a way to get AudioUnit to report an error at all, so
here's a crappy hack that takes care of this in most cases. We assume
that all devices have a kAudioDevicePropertyDeviceIsAlive property.
Invalid devices will error when querying the property (with 'obj!' as
status code).
This is not the correct fix, because we try to double-guess AudioUnit's
behavior by accessing a lower label API. Suggestions welcome.
This helps with shitty APIs and even shittier drivers (I'm looking at
you, ALSA). Sometimes they won't send proper wakeups. This can be fine
during playback, when for example playing video, because mpv still will
wakeup the AO outside of its own wakeup mechanisms when sending new data
to it. But when draining, it entirely relies on the driver's wakeup
mechanism. So when the driver wakeup mechanism didn't work, it could
hard freeze while waiting for the audio thread to play the rest of the
data.
Avoid this by waiting for an upper bound. We set this upper bound at the
total mpv audio buffer size plus 1 second. We don't use the get_delay
value, because the audio API could return crap for it, and we're being
paranoid here. I couldn't confirm whether this works correctly, because
my driver issue fixed itself.
(In the case that happened to me, the driver somehow stopped getting
interrupts. aplay froze instead of playing audio, and playing audio-only
files resulted in a chop party. Video worked, for reasons mentioned
above, but drainign froze hard. The driver problem was solved when
closing all audio output streams in the system. Might have been a dmix
related problem too.)
When we're draining, don't wakeup the core on every buffer fill, since
unlike during normal playback, we won't actually get more data. The
wakeup here conceptually works like wakeups with condition variables, so
redundant wakeups do not hurt, so this is just a minor change and
nothing of consequence.
(Final EOF also requires waking up the core, but there is separate code
to send this notification.)
Also dump the p->still_playing field in trace logging.
For clang, it's enough to just put (void) around usages we are
intentionally ignoring the result of.
Since GCC does not seem to want to respect this decision, we are forced
to disable the warning globally.
Since the main thread is shared by other things in the player, using STA (single
threaded aparement) may have caused problems. Instead initialize in MTA
(multithreaded apartment).
This reportedly makes it work on ODROID-C2. The idea for this hack is
taken from kodi; they unconditionally set some or all of those flags.
I don't trust ALSA enough to hope that setting these flags couldn't
break something else, so we try without them first.
It's not clear whether this is a driver bug or a bug in the ALSA libs.
There is no ALSA bug tracker (the ALSA website has had a dead link to
a deleted bug tracker fo years). There's not much we can do other than
piling up ridiculous hacks. At least I think that at this point invalid
API usage by mpv can be excluded as a cause.
ALSA might be the worst audio API ever.
Including initguid.h at the top of a file that uses references to GUIDs
causes the GUIDs to be declared globally with __declspec(selectany). The
'selectany' attribute tells the linker to consolidate multiple
definitions of each GUID, which would be great except that, in Cygwin
and MinGW GCC 6.1, this method of linking makes the GUIDs conflict with
the ones declared in libuuid.a.
Since initguid.h obsoletes libuuid.a in modern compilers that support
__declspec(selectany), add initguid.h to all files that use GUIDs and
remove libuuid.a from the build.
Fixes#3097
Setting this here is a race condition. It's called from a CoreAudio
callbacks, and there are no locks. It's a string, so this can be
potentially severe.
It's hard to fix and only CoreAudio supported it, so remove it.
This causes the "audio-out-detected-device" property to return nothing
on all platforms.
This is particularly useful for opus which allows only a fairly restrictive set
of samplerates. If the codec doesn't provide a list of samplerates, just
continue to try the requsted one and hope for the best.
fixes#2957
This eliminates some intermittent pops heard in a HRT MicroStreamer DAC
uncorrelated with user interaction. As a bonus, this resolves#1773 which I can
o longer reproduce as of this commit. Leave the 50ms buffer for shared mode
since that seems to be working quite well.
This is also the way exclusive mode is done in the MSDN example code:
https://msdn.microsoft.com/en-us/library/windows/desktop/dd370844%28v=vs.85%29.aspx
This was originally increased in c545c40 to mitigate glitches that subsequent
refactorings have eliminated.
A COM message loop is apparently totally inappropriate for a low latency
thread. It leads to audio glitches because the thread doesn't wake up fast
enough when it should. It also causes mysterious correlations between the vo
and ao thread (i.e., toggling fullscreen delays audio feed events). Instead use
an mp_dispatch_queue to set/get volume/mute/session display name from the audio
thread. This has the added benefit of obviating the need to marshal the
associated interfaces from the audio thread.
Don't wait for WASAPI to send another feed event if we detect an underfull
buffer. It seems that WASAPI doesn't always send extra feed events if
something causes rendering to fall behind. This causes every subsequent playback
buffer to under-run until playback is reset. The fix is simply to do a one-shot
double feed when this happens, which allows rendering to catch up with playback.
This was observed to happen when using MsgWaitForMultipleObjects to wait for the
feed event and toggling fullscreen with vo=opengl:backend=win. This commit
improves the behaviour in that specific case and more generally makes exclusive
mode significantly more robust.
This commit also moves the logic to avoid *over*filling the exclusive mode
buffer into thread_feed right next to the above described underfil logic.
OpenSL ES is used on Android. At the moment only stereo output is
supported. Two options are supported: 'frames-per-buffer' and
'sample-rate'. To get better latency the user of libmpv should pass
values obtained from AudioManager.getProperty(PROPERTY_OUTPUT_FRAMES_PER_BUFFER)
and AudioManager.getProperty(PROPERTY_OUTPUT_SAMPLE_RATE).
I can't explain this, but it seems to be a similar case to the ALSA HDMI
one. I find it hard to tell because of the slightly different names and
conventions in use in libavcodec, WAVEEXT channel masks, decoders, codec
specifications, HDMI, and platform audio APIs.
The fix is the same as the one for ao_alsa (see commit be49da72). This
should fix at least playing 7.1 sources on OSX with 7.1(rear) selected
in Audio MIDI Setup. The ao_alsa commit mentions XBMC, but I couldn't
find out where it does that or if it also does that for CoreAudio. It's
woth noting that PHT (essentially an old XBMC fork) also exhibited the
incorrect behavior (i.e. side and back speakers were swapped).
Correctly avoid a reload if the current device was specified by the user through
--audio-device. Previously, we only recognized if the user had specified
--ao=wasapi:device=.
Notably, the address of the enumerator->count member is passed to
IMMDeviceCollection::GetCount(), which expects a UINT variable, not an int. How
did this ever work?
Previously, if the enumerator found no devices, attempting to get the default
device with IMMDeviceEnumerator::GetDefaultAudioEndpoint would result in the
cryptic (and undocumented) E_PROP_ID_UNSUPPORTED. This way, the user is given a
better indication of what exactly is wrong and isolates any other possible
triggers for this error.
While the situation is not really clear for the other rewritten
coreaudio code, it's very clear for the channel mapping code. It was all
written by us. (MPlayer doesn't even have any channel map handling.)
This covers source files which were added in mplayer2 and mpv times
only, and where all code is covered by LGPL relicensing agreements.
There are probably more files to which this applies, but I'm being
conservative here.
A file named ao_sdl.c exists in MPlayer too, but the mpv one is a
complete rewrite, and was added some time after the original ao_sdl.c
was removed. The same applies to vo_sdl.c, for which the SDL2 API is
radically different in addition (MPlayer supports SDL 1.2 only).
common.c contains only code written by me. But common.h is a strange
case: although it originally was named mp_common.h and exists in MPlayer
too, by now it contains only definitions written by uau and me. The
exceptions are the CONTROL_ defines - thus not changing the license of
common.h yet.
codec_tags.c contained once large tables generated from MPlayer's
codecs.conf, but all of these tables were removed.
From demux_playlist.c I'm removing a code fragment from someone who was
not asked; this probably could be done later (see commit 15dccc37).
misc.c is a bit complicated to reason about (it was split off mplayer.c
and thus contains random functions out of this file), but actually all
functions have been added post-MPlayer. Except get_relative_time(),
which was written by uau, but looks similar to 3 different versions of
something similar in each of the Unix/win32/OSX timer source files. I'm
not sure what that means in regards to copyright, so I've just moved it
into another still-GPL source file for now.
screenshot.c once had some minor parts of MPlayer's vf_screenshot.c, but
they're all gone.
Previously used opt_exclusive option to decide which volume control code to run.
The might not always reflect the actual state, for example if passthrough
is used. Admittedly, none of the volume controls will work anyway with
passthrough, but this is the right thing to do.
Note that hresult_to_str() (coming from wasapi_explain_err()) is mostly
wasapi-specific, but since HRESULT error codes are unique, it can be
extended for any other use.
It existed for XP-compatibility only. There was also a time where
ao_wasapi caused issues, but we're relatively confident that ao_wasapi
works better or at least as good as ao_dsound on Windows Vista and
later.
Normally, PulseAudio accepts any combination of sample format, sample
rate, channel count/map. Sometimes it does not. For example, the channel
rate or channel count have fixed maximum values. We should not fail
fatally in such cases, but attempt to fall back to a working format.
We could just send pass an "unset" format to Pulse, but this is not too
attractive. Pulse could use a format which we do not support, and also
doing so much for an obscure corner case is not reasonable. So just pick
a format that is very likely supported.
This still could fail at runtime (the stream could fail instead of going
to the ready state), but this sounds also too complicated. In
particular, it doesn't look like pulse will tell us the cause of the
stream failure. (Or maybe it does - but I didn't find anything.)
Last but not least, our fallback could be less dumb, and e.g. try to fix
only one of samplerate or channel count first to reduce the loss, but
this is also not particularly worthy the effort.
Fixes#2654.
Unify and clean up listing and selection. Use common enumerator code for both
operations to avoid duplication or inconsistencies.
Maintain, but significatnly simplify manual device selection by id, name or
number. This actually fixes loading by name which didn't really work before
since the "name" displayed by --audio-device=help differed from that used to
match the selection, which used the device "description" instead.
Save the selected deviceID in the private structure for later loading. This will
permit moving the device selection into the main thread in a future commit.
Apparently it's only wine where the qpc_position returned by
IAudioClock_GetPosition can be overflowed. So actually do the rescaling
correctly, but throw away the result if it looks unreasonable.
this fixes a regression in 5afa68835a
Make sure that subtraction of performance counters is done correctly.
Follow the *exact* instructions for converting performance counter to something
comparable to the QPCposition returned by IAudioClient::GetPosition
https://msdn.microsoft.com/en-us/library/windows/desktop/dd370889%28v=vs.85%29.aspx
Also make sure that subtraction of unsigned integers is stored into a signed
integer to avoid nastiness. Also be more careful about overflow in the
conversion of the device position into number of samples.
Avoid casting mp_time_us() to a double, and use llrint to convert the
double precision delay_us back to integer for ao_read_data.
Finally, actually check the return value of ao_read_data and add a verbose
message if it is not the expected value. Unfortunately,
there is no way to tell WASAPI when this happens since the frame_count in
ReleaseBuffer must match GetBuffer.
Do not try and set/get master volume in exclusive if there is no
hardware support. This would just uselessly change the master slider,
but have no effect on the actual volume.
Furthermore if getting hardware volume support information fails, then assume
it has none.
It was complicated and not even very intuitive to the user.
If you are controlling the master volume, you just have to be
prepared to deal with the consequences.
If there were many AO drivers without device selection, this added a
"Default" entry for each AO. These entries were not distinguishable, as
the device list feature is meant not to require to display the "raw"
device name in GUIs.
Disambiguate them by adding the driver name. If the AO is the first, the
name will remain just "Default". (The condition checks "num > 1",
because the very first entry is the dummy for AO autoselection.)
Remove known useless device entries from the --audio-device list (and
corresponding property). Do this because the list is supposed to be a
high level list of devices the user can select. ALSA does not provide
such a list (in an useable manner), and ao_alsa.c is still in the best
position to improve the situation somewhat.
The ALSA doxygen says:
IOID - input / output identification ("Input" or "Output"), NULL
means both
This bug was blatantly introduced with commit cf94fce4.
Apparently, some audio drivers do not support the DTS subtype, but
passthrough works anyway if the AC3 subtype is set. Just retry with
AC3 if the proper format doesn't work. The audio device which
exposed this behavior reported itself as
"M601d-A3/A3R (Intel(R) Display Audio)".
xbmc/kodi even always passes DTS as AC3.
Essentially we'd use something random, just because it's part of the srt
of traditionally used ALSA channel mappings. But each driver can do its
own things.
This doesn't let me sleep at night, so remove it.
We need to effectively swap the last channel pair. See commit 4e358a96
and 5a18c5ea for details.
Doing this seems rather strange, as 7.1 just extends 5.1 with 2 new
speakers, and 5.1 doesn't need this change. Going by the HDMI standard
and the Intel HDA sources (cited in the referenced commits), it also
looks like 7.1 should simply append two channels to 5.1 as well. But
swapping them is apparently correct. This is also what XBMC does. (I
didn't find any other applications doing 7.1 PCM using the ALSA channel
map API. VLC seems to ignore the 7.1 case.) Testing reveals that at
least the end result is correct.
"Normal" ALSA 7.1 is unaffected by this, as it reports a different
(and saner) channel layout.
Instead of constructing an ALSA channel map from mpv ones from scratch,
try to find the original ALSA channel map again. Th result is that we
need to convert channel maps only in one direction. If we need to map
a mp_chmap to ALSA, we fetch the device's channel map list, convert
each entry to mp_chmap, and find the first one which fits.
This seems helpful for the following commit. For now, this only gets rid
of mapping back the trivial MONO mapping, which alone would still be
acceptable, but with other channel layout mogrifications it gets messy
fast. While we need to do something awkward to keep our channel map
reordering for VAR chmaps (which basically gives nicer output and
possibly slightly better performance), this is still the better
solution.
These calls actually can leave the ALSA configuration space empty (how
very useful), which is why snd_pcm_hw_params() can fail. An earlier
change intended to make this non-fatal, but it didn't work for this
reason.
Backup the old parameters, so we can retry with the non-empty
configuration space. (It has to be non-empty, because the previous
setters didn't fail.)
Note that the buffer settings are not very important to us. They're
a leftover from MPlayer, which needed to write enough data to the
audio device to not underrun while decoding and displaying a video
frame. In mpv, most of these things happen asynchronously, _and_
there is a dedicated thread just for feeding the audio device, so
we should be pretty imune even against extreme buffer settings. But
I suppose it's still useful to prevent PulseAudio from making the
buffer too large, so still keep this code.
Again, this could have bad access, is unlikely, and has no bad
consequences. It's noteworthy that vlc and the ALSA PCM example both do
this first, even if they set the sample rate later.
