BBufferProducer¶
Constructor and Destructor¶
BBufferProducer()
explicit BBufferProducer::BBufferProducer(media_type producerType)
Constructs the BBufferProducer object. The producerType specifies the type of media data that will be output by the node.
If the node will produce more than one type of data, your BBufferProducer subclass should set the kind to the default (which is a wildcard value).
If your node has additional latency on startup, you should call
SetInitialLatency() to record this
information. This might be the case if the buffers your node produces are
created from an input signal which refreshes infrequently, such as a
television signal.
Note
In BeOS Release 4.5.2 and earlier, the producerType has a default value; it no longer does, and you’ll have to specify the media type yourself.
Member Functions¶
AdditionalBufferRequested()
virtual status_t BBufferProducer::AdditionalBufferRequested(const media_source &source, media_buffer_id previousBufferID, bigtime_t previousTime, const media_seek_tag *previousTag)
When a consumer calls
BBufferConsumer::RequestAdditionalBuffer(), this function is
called as a result. Its job is to call
SendBuffer() to immediately send the next
buffer to the consumer.
The previousBufferID, previousTime, and previousTag arguments identify the last buffer the consumer received. Your node should respond by sending the next buffer after the one described.
Note
The previousTag may be NULL.
Return B_OK if all is well; otherwise return an
appropriate error code.
ChangeFormat()
status_t BBufferProducer::ChangeFormat(const media_source &source, const media_destination &destination, media_format *newFormat)
Informs the destination that the data flowing between source and destination is immediately changing to the format specified by newFormat.
Warning
You must never call SendBuffer() while this
call is pending.
Return Code |
Description |
|---|---|
|
The format change request has been sent without error. |
|
A mutual exclusion error has occurred with
|
Other errors. |
You may receive other errors if the consumer doesn’t agree with the new format you’re requesting. |
ClipDataToRegion()
static status_t BBufferProducer::ClipDataToRegion(int32 format, int32 byteCount, const void *clipData, BRegion *region)
Given byteCount bytes of clipping data clipDatain the specified format, makes the specified region match the clipping region.
The region you specify must already exist.
The only format currently supported is B_CLIP_SHORT_RUNS.
Return Code |
Description |
|---|---|
|
The clip data was converted without error. |
|
The specified clip format is invalid. |
See also: BBufferConsumer::RegionToClipData()
Connect()
virtual void BBufferProducer::Connect(status_t status, const media_source &source, const media_destination &destination, const media_format &format, char *ioName)
Implement this hook function to establish a connection between the source and the destination. The format negotiation is already complete by the time Connect() is called, so you have to accept the specified format.
The status argument indicates whether or not the connection
actually took place; this is the result code returned by the
BBufferConsumer::Connected() function or an error code
indicating an error that has occurred during other preparation for the
connection.
If status isn’t B_OK, you should release the
media_source that was reserved for this connection by
PrepareToConnect(); this lets it be used by
other connection attempts.
On entry, ioName contains the connection name specified by the
consumer (this may be different from the name specified by the
PrepareToConnect() function). On return,
ioName should point to a name for the connection; if the name
really matters to you, copy the name you want the connection to have back
into ioName; otherwise, you can leave it alone.
Disconnect()
virtual void BBufferProducer::Disconnect(const media_source &source, const media_destination &destination) = 0
Your implementation of Disconnect() should terminate the connection between the specified source and destination. Once you return from this function, you shouldn’t send any further buffers on the connection.
If a BBufferGroup has been specified for your producer (via
the SetBufferGroup() function), you should
delete it here.
DisposeOutputCookie()
virtual status_t BBufferProducer::DisposeOutputCookie(int32 cookie) = 0
Once a client has finished iterating through your outputs via
GetNextOutput() calls, it will call this
function with the last value you returned as a cookie. This gives
you the opportunity to dispose of any memory you may have allocated for the
iteration process.
Return B_OK if the cookie is successfully disposed of (or
if nothing needs to be done); otherwise, return an appropriate error code.
EnableOutput()
virtual void BBufferProducer::EnableOutput(const media_source &whichOutput, bool enabled, int32 *_deprecated_) = 0
This hook function is called when a consumer’s
SetOutputEnabled() function is called. This
indicates whether or not the output specified by whichOutput
needs to be sent buffers. You must implement this function so that you
don’t send buffers to outputs that don’t need them. The
_deprecated_ argument is no longer used.
By default, output is enabled.
FindLatencyFor()
status_t BBufferProducer::FindLatencyFor(const media_destination &forDestination, bigtime_t *outLatency, media_node_id *outTimeSource) = 0
FindLatencyFor() returns the latency introduced by sending data to the destination forDestination. On return, the latency will be stored in outLatency, and the time source used by forDestination will be available in outTimeSource (unless an error is returned, in which case these values are undetermined).
The latency of sending a buffer from one time source to another should always be assumed to be zero, since there may be no relationship between the progress of time of two different time sources.
Return Code |
Description |
|---|---|
|
The latency was returned without error. |
|
The destination is invalid. |
Port errors. |
The request couldn’t be sent to the destination. |
FindSeekTag()
status_t BBufferProducer::FindSeekTag(const media_destination &forDestination, bigtime_t inTargetTime, media_seek_tag *outTag, bigtime_t *outTaggedTime, uint32 *outFlags = 0, uint32 *inFlags = 0)
In order to improve seek performance, the Media Kit provides the concept of seek tags. These are special tags that identify easily-located points in media data (such as key frames in Cinepak video). The FindSeekTag() function asks the consumer specified by forDestination for the nearest seek tag to the time specified by inTargetTime, and returns the tag in outTag and the time corresponding to that tag in outTaggedTime. On return, outFlags (if the pointer isn’t NULL) contains flags giving further details about the tag.
There are currently no defined values for inFlags or outFlags.
Return Code |
Description |
|---|---|
|
No error. |
Port errors. |
An error occurred communicating with the Media Server. |
FormatChangeRequested()
virtual status_t BBufferProducer::FormatChangeRequested(const media_source &source, const media_destination &destination, media_format *ioFormat, int32 *_deprecated_) = 0
Implement FormatChangeRequested() to change the format of the media data flowing from the given source to the specified destination to the format specified by ioFormat. If there are wildcards specified in ioFormat, fill them in to match the format you prefer before returning from this call. You should ignore the _deprecated_ argument; it’s no longer used.
Warning
This call is issued synchronously by the destination, so you can’t ask it if the format is acceptable. Fortunately, since the destination issued the request, you can safely assume that it’s fine.
Return B_OK if the change request is processed
successfully; otherwise, return an appropriate error code.
See also: FormatSuggestionRequested(),
FormatProposal()
FormatProposal()
virtual status_t BBufferProducer::FormatProposal(const media_source &output, media_format *format) = 0
Your BBufferProducer should implement this function to verify that the proposed media_format is suitable for the specified output. If any fields in the format are wildcards, and you have a specific requirement, adjust those fields to match your requirements before returning.
Return B_OK if the proposed format is acceptable; once
you’ve done so, the Media Kit will assume that any connection request made
on output with the specified format (after any changes you may have made)
will succeed.
Constant |
Description |
|---|---|
|
output isn’t available. |
|
format isn’t reasonable. |
FormatSuggestionRequested()
virtual status_t BBufferProducer::FormatSuggestionRequested(media_type type, int32 quality, media_format *format) = 0
You must implement FormatSuggestionRequested() to return fill the buffer pointed to by format that your producer is capable of emitting that meets the desired type and quality requirements.
If your producer can work with a range of possible formats, let the quality argument guide your selection. For example, you might choose to use 10 fps for previews, and 60 fps interlaced 640x480 for full-quality video.
If type is a media class that your producer doesn’t want to work
with, return B_BAD_MEDIA_FORMAT. If you’re preapared to
accept a wide range of values for some specific field, set that field to
the wildcard value (see media_audio_format::wildcard() and
media_video_format::wildcard() for more information.
Return B_OK if the format is successfully
returned.
GetLatency()
virtual status_t BBufferProducer::GetLatency(bigtime_t *outLatency) = 0
Implement this hook function to store, in outLatency, the total amount of latency your BBufferProducer incurs from receiving a buffer of data until it reaches its ultimate destination.
Call FindLatencyFor() on whatever outputs the
data is being forwarded to, add your own latency to the largest of those
values, and return that value.
The default implementation of GetLatency() finds the maximum latency of your currently-available outputs by iterating over them, and returns that value in outLatency; therefore, your implementation of this function may simply need to call the inherited version of this function, then add your own processing latency to the returned value.
Return Code |
Description |
|---|---|
|
The latency has been returned successfully. |
Other errors. |
Unable to calculate the latency. |
GetNextOutput()
virtual status_t BBufferProducer::GetNextOutput(int32 *cookie, media_output *outOutput) = 0
Implement this function to return information about your available outputs. The first time it’s called for a new iteration loop, the value pointed to by cookie will be 0. Each time GetNextOutput() is called, you should set it to some value that makes sense to you so you can keep track of where in the iteration process the client is, but never set it to 0.
For each call to GetNextOutput(), including the first, you should return one of your outputs that the client hasn’t seen during the iteration loop in outOutput.
Once all outputs have been reported, you should return
B_ERROR.
HandleMessage()
virtual status_t BBufferProducer::HandleMessage(int32 message, const void *data, size_t size)
When your node derived from BBufferProducer receives a message on
its control port, you should handle it yourself if you know how, or
dispatch to each ancestor class in turn (starting with
BBufferProducer’s HandleMessage()) until one of the
HandleMessage() implementations returns B_OK.
If none of the inherited implementations of this function returns
B_OK, you should pass the message to
BMediaNode::HandleBadMessage() to be dealt with.
Your port-listening thread should call HandleMessage() to dispatch the received data.
See also: “About Multiple Virtual Inheritance”
LatencyChanged()
virtual void BBufferProducer::LatencyChanged(const media_source &source, const media_destination &destination, bigtime_t newLatency, uint32 flags)
This hook function is called when a BBufferConsumer that’s
receiving data from you determines that its latency has changed. It will
call its BBufferConsumer::SendLatencyChange() function, and in
response, the Media Server will call your LatencyChanged()
function.
The source argument indicates your output that’s involved in the connection, and destination specifies the input on the consumer to which the connection is linked. newLatency is the consumer’s new latency. The flags are currently unused.
Override this function to implement whatever functionality you need to adjust your own latency calculations to keep the data flowing smoothly.
LateNoticeReceived()
virtual void BBufferProducer::LateNoticeReceived(const media_source &whichSource, bigtime_t howLate, bigtime_t performanceTime) = 0
This hook function is called when a BBufferConsumer that’s
receiving data from you determines that data is arriving late (when the
BBufferConsumer::NotifyLateProducer() function is called); the
exact degree to which your buffers are late is specified by the
howLate argument. Your implementation of this function should
take whatever steps are necessary to correct the problem, either by asking
nodes upstream from you to deliver buffers earlier, dropping buffers, or
other appropriate actions, depending on the current run mode.
The performanceTime argument specifies the performance time at which the notification was sent.
See also: BMediaNode::RunMode()
PrepareToConnect()
virtual status_t BBufferProducer::PrepareToConnect(const media_source &whichSource, const media_destination &whichDestination, media_format *format, media_source *outSource, char *outName) = 0
The PrepareToConnect() hook is called before a new connection between the source whichSource and the destination whichDestination is established, in order to give your producer one last chance to specialize any wildcards that remain in the format (although by this point there shouldn’t be any, you should check anyway).
Your implementation should, additionally, return in outSource the
source to be used for the connection, and should fill the outName
buffer with the name the connection will be given; the consumer will see
this in the outInput->name argument specified to
BBufferConsumer::Connected(). If your node doesn’t care what
the name is, you can leave the outName untouched.
Note
Your Connect() function may return a
different media_source value in outOutput’s source field
than the one specified as the source argument to this function.
One reason you might do this is if you implement one media_source
to accept connection requests, then create a new media_source to
actually handle each connection.
Return B_OK if the connection process should proceed, or
an appropriate error code if something’s wrong.
If you return B_OK, the consumer’s
Connected() function will be called, to let
it know that a new connection is being established. Finally, the producer’s
Connect() function is called to complete the exchange.
ProducerType()
media_type BBufferProducer::ProducerType()
Returns the media_type of the media data produced by the node.
ProposeFormatChange()
status_t BBufferProducer::ProposeFormatChange(media_format *format, const media_destination &forDestination)
Call this function to determine whether or not the destination forDestination is prepared to accept buffers in the specified format. This function can be especially useful if you want to test various formats to select the best compatible format during a hookup request in which the requested format contains wildcards.
Return Code |
Description |
|---|---|
|
The proposed format is acceptable to the destination. |
Other errors. |
The proposed format is unacceptable, or an error occurred in querying the destination node. |
SendBuffer()
status_t BBufferProducer::SendBuffer(BBuffer *buffer, media_destination &destination)
Call this function to send a buffer of media data to the specified
destination, which must already be connected to one of your
outputs. This is how your BBufferProducer object will send data
downstream to BBufferConsumers to which it’s connected.
It’s your responsibility to ensure that the buffer’s header and the data contained in the buffer itself are valid, although SendBuffer() will automatically fill out the following header fields for you:
buffer
for_id
change_tag
In particular, be sure that if you’re outputting video buffers you set the media_video_buffer to describe the video properly. If you don’t, things will go badly for you.
You can obtain a buffer to fill and send by calling
BBufferConsumer::RequestAdditionalBuffer() on a
BBufferConsumer that you own (and that’s okay to use for
buffers going to the specified destination).
Return Code |
Description |
|---|---|
|
The buffer was sent without error. |
Port errors. |
An error occurred sending the buffer. |
SendDataStatus()
status_t BBufferProducer::SendDataStatus(int32 status, media_destination &destination, bigtime_t atTime)
Call this function to inform the specified destination whether or not there’s data available from your producer node. Specify the appropriate status flag as the status argument, and the time at which the status takes effect as the atTime argument.
Possible values for the status argument are:
Constant |
Description |
|---|---|
|
There aren’t any buffers ready for the destination. |
|
There are buffers ready for the destination. |
|
The producer has stopped. |
Return Code |
Description |
|---|---|
|
The status update was sent without error. |
Port errors. |
The status update couldn’t be delivered. |
SetBufferGroup()
virtual status_t BBufferProducer::SetBufferGroup(const media_source &forSource, BBufferGroup *group) = 0
When a client wants a specific BBufferGroup to be used for a
given output forSource, it will call this function. You should
remember the group and use it for all requests for buffers to
send on the output forSource (and for no other outputs, unless the client
explicitly requests you do so by calling SetBufferGroup() for
another output source).
If your BBufferProducer goes away, or the connection is broken,
delete the BBufferGroup object.
If group is NULL, you should use whatever
BBufferGroup you wish after disposing of the previous group.
It’s okay to pass group on to another node upstream from your
BBufferProducer if your BBufferProducer only passes
along buffers it receives in its processing loop; in that case, you’re not
really the owner of the BBufferGroup, unless you pass
true for willReclaim in the call to
BBufferConsumer::SetOutputBuffersFor().
Return B_OK if the buffer group is set without incident;
otherwise, return an appropriate error code.
SetInitialLatency()
void BBufferProducer::SetInitialLatency(bigtime_t initialLatency, uint32 flags) = 0
If your node has additional startup latency imposed by the signal from which its buffers are constructed, you should call SetInitialLatency() to specify the maximum possible latency that can be added by this delay. initialLatency should be the maximum latency, in microseconds, that might occur.
One situation in which this occurs is for TV capture card nodes. An NTSC television signal broadcasts a new field about every sixtieth of a second, which means that if your node is started partway through one field being received, you might have to wait as long as a sixtieth of a second for the first complete frame to arrive. So the maximum latency in this situation is a sixtieth of a second.
Setting the initial latency correctly can prevent consumers from having problems synchronizing with your node, and can improve performance.
flags should be 0 for now; there are no values defined yet.
SetPlayRate()
virtual status_t BBufferProducer::SetPlayRate(int32 numerator, int32 denominator)
This function is called to tell the producer to resample the data rate by the specified factor. Specifying a value of 1 (ie, numerator/denominator = 1) indicates that the data should be output at the same playback rate that it comes into the node at. The format of the data should be unchanged.
For example, if you’re playing a sound at 48 kHz, and you receive a call to SetPlayRate() with a numerator of 2 and a demoninator of 1 (double speed), you should resample so that you move twice as fast through the source data while keeping the output rate constant. You might do this by doing a brute-force resample to 24 kHz (which would result in twice the data rate) or do time-compression (which would retain the pitch).
As another example, if you’re playing video at 30 frames per second, and your SetPlayRate() function is called with a ratio of 1:2 specified (half speed), you should continue sending 30 frames per second, but you need to arrange for the playback to look like half-speed. A reasonable way to do this would be to send each frame twice (re-time-stamped and buffered internally, if necessary), which would result in the desired half-speed appearance.
Return B_OK if the sampling rate is changed; otherwise,
return an error. It’s okay to return an error if you don’t support varying
sampling rates—the Media Kit won’t hold that against you.
VideoClippingChanged()
virtual status_t BBufferProducer::VideoClippingChanged(const media_source &forSource, int16 numShorts, int16 *clipData, const media_video_display_info &display, int32 *outFromChangeTag) = 0
This hook function is called when a client wants your BBufferProducer to output video data clipped to a particular region. Your producer must remember this clipping region and apply it to all video data you produce, without altering any bytes outside the region in any buffers sent through the source forSource.
Before your implementation of VideoClippingChanged() returns, you should set the value pointed to by outFromChangeTag to the change tag value at which the clipping will take effect, so the client will know what buffers it can expect to have the requested clipping. This can be done easily by adding the following line to your implementation:
*outFromChangeTag = UpdateChangeTag();
You can use the ClipDataToRegion() function
to convert the data in clipData into an actual
BRegion if that’s a better format for you to work with. If you
do, keep in mind that numShorts is the actual number of
int16 values in the array specified by clipData, while
ClipDataToRegion() requires the number of
bytes of data in the array; be sure to multiply numShorts by
sizeof(int16).
The media_video_display_info structure referred to by display indicates the format of the video display onto which the video is being displayed; this lets you know what color space, screen size, and so forth is in use on the video display, so your producer can render properly. VideoClippingChanged() is called not only when clipping changes, but when the configuration of the display changes as well. Your producer must abide by this starting at the specified change count.
See “Video Clipping” for information on the format of the clip data.
Constants¶
Clipping Data Formats¶
Declared in: media/BufferProducer.h
Constant |
Description |
|---|---|
|
Clipping is encoded using runs of shorts. |
This value defines the only clipping format currently supported by
BBufferProducer. Note that because this constant is a member of
the BBufferProducer class, if you need to access it from other
classes, you must code it as BBufferProducer::B_CLIP_SHORT_RUNS. See
“Video Clipping” for a description of this format.
suggestion_quality¶
Declared in: media/BufferProducer.h
Constant |
Description |
|---|---|
|
Any quality. |
|
A low quality level (10). |
|
Medium quality level (50). |
|
High quality level (100). |
Quality values you can use when you don’t want to have to come up with one on your own.