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merge and deduplicate some pa_buffer_attr documentation

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jnqnfe 2017-09-08 04:31:42 +01:00 • committed by Tanu Kaskinen
parent b683350856
commit 26b1d0fc84
2 changed files with 44 additions and 78 deletions
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46
src/pulse/def.h
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@ -401,13 +401,18 @@ typedef struct pa_buffer_attr {
uint32_t tlength; uint32_t tlength;
/**< Playback only: target length of the buffer. The server tries /**< Playback only: target length of the buffer. The server tries
* to assure that at least tlength bytes are always available in * to assure that at least tlength bytes are always available in
* the per-stream server-side playback buffer. It is recommended * the per-stream server-side playback buffer. The server will
* to set this to (uint32_t) -1, which will initialize this to a * only send requests for more data as long as the buffer has
* value that is deemed sensible by the server. However, this * less than this number of bytes of data.
* value will default to something like 2s, i.e. for applications *
* that have specific latency requirements this value should be * It is recommended to set this to (uint32_t) -1, which will
* set to the maximum latency that the application can deal * initialize this to a value that is deemed sensible by the
* with. When PA_STREAM_ADJUST_LATENCY is not set this value will * server. However, this value will default to something like 2s;
* for applications that have specific latency requirements
* this value should be set to the maximum latency that the
* application can deal with.
*
* When PA_STREAM_ADJUST_LATENCY is not set this value will
* influence only the per-stream playback buffer size. When * influence only the per-stream playback buffer size. When
* PA_STREAM_ADJUST_LATENCY is set the overall latency of the sink * PA_STREAM_ADJUST_LATENCY is set the overall latency of the sink
* plus the playback buffer size is configured to this value. Set * plus the playback buffer size is configured to this value. Set
@ -421,11 +426,19 @@ typedef struct pa_buffer_attr {
* playback before at least prebuf bytes are available in the * playback before at least prebuf bytes are available in the
* buffer. It is recommended to set this to (uint32_t) -1, which * buffer. It is recommended to set this to (uint32_t) -1, which
* will initialize this to the same value as tlength, whatever * will initialize this to the same value as tlength, whatever
* that may be. Initialize to 0 to enable manual start/stop * that may be.
* control of the stream. This means that playback will not stop *
* on underrun and playback will not start automatically. Instead * Initialize to 0 to enable manual start/stop control of the stream.
* pa_stream_cork() needs to be called explicitly. If you set * This means that playback will not stop on underrun and playback
* this value to 0 you should also set PA_STREAM_START_CORKED. */ * will not start automatically, instead pa_stream_cork() needs to
* be called explicitly. If you set this value to 0 you should also
* set PA_STREAM_START_CORKED. Should underrun occur, the read index
* of the output buffer overtakes the write index, and hence the
* fill level of the buffer is negative.
*
* Start of playback can be forced using pa_stream_trigger() even
* though the prebuffer size hasn't been reached. If a buffer
* underrun occurs, this prebuffering will be again enabled. */
uint32_t minreq; uint32_t minreq;
/**< Playback only: minimum request. The server does not request /**< Playback only: minimum request. The server does not request
@ -444,11 +457,12 @@ typedef struct pa_buffer_attr {
* but decrease control overhead. It is recommended to set this to * but decrease control overhead. It is recommended to set this to
* (uint32_t) -1, which will initialize this to a value that is * (uint32_t) -1, which will initialize this to a value that is
* deemed sensible by the server. However, this value will default * deemed sensible by the server. However, this value will default
* to something like 2s, i.e. for applications that have specific * to something like 2s; For applications that have specific
* latency requirements this value should be set to the maximum * latency requirements this value should be set to the maximum
* latency that the application can deal with. If * latency that the application can deal with.
* PA_STREAM_ADJUST_LATENCY is set the overall source latency will *
* be adjusted according to this value. If it is not set the * If PA_STREAM_ADJUST_LATENCY is set the overall source latency
* will be adjusted according to this value. If it is not set the
* source latency is left unmodified. */ * source latency is left unmodified. */
} pa_buffer_attr; } pa_buffer_attr;

76
src/pulse/stream.h
View file

@ -92,68 +92,20 @@
* overflows/underruns. * overflows/underruns.
* *
* The buffer metrics may be controlled by the application. They are * The buffer metrics may be controlled by the application. They are
* described with a pa_buffer_attr structure which contains a number * described with a pa_buffer_attr structure.
* of fields:
*
* \li maxlength - The absolute maximum number of bytes that can be
* stored in the buffer. If this value is exceeded
* then data will be lost. It is recommended to pass
* (uint32_t) -1 here which will cause the server to
* fill in the maximum possible value.
*
* \li tlength - The target fill level of the playback buffer. The
* server will only send requests for more data as long
* as the buffer has less than this number of bytes of
* data. If you pass (uint32_t) -1 (which is
* recommended) here the server will choose the longest
* target buffer fill level possible to minimize the
* number of necessary wakeups and maximize drop-out
* safety. This can exceed 2s of buffering. For
* low-latency applications or applications where
* latency matters you should pass a proper value here.
*
* \li prebuf - Number of bytes that need to be in the buffer before
* playback will commence. Start of playback can be
* forced using pa_stream_trigger() even though the
* prebuffer size hasn't been reached. If a buffer
* underrun occurs, this prebuffering will be again
* enabled. If the playback shall never stop in case of a
* buffer underrun, this value should be set to 0. In
* that case the read index of the output buffer
* overtakes the write index, and hence the fill level of
* the buffer is negative. If you pass (uint32_t) -1 here
* (which is recommended) the server will choose the same
* value as tlength here.
*
* \li minreq - Minimum number of free bytes in the playback
* buffer before the server will request more data. It is
* recommended to fill in (uint32_t) -1 here. This value
* influences how much time the sound server has to move
* data from the per-stream server-side playback buffer
* to the hardware playback buffer.
*
* \li fragsize - Maximum number of bytes that the server will push in
* one chunk for record streams. If you pass (uint32_t)
* -1 (which is recommended) here, the server will
* choose the longest fragment setting possible to
* minimize the number of necessary wakeups and
* maximize drop-out safety. This can exceed 2s of
* buffering. For low-latency applications or
* applications where latency matters you should pass a
* proper value here.
* *
* If PA_STREAM_ADJUST_LATENCY is set, then the tlength/fragsize * If PA_STREAM_ADJUST_LATENCY is set, then the tlength/fragsize
* parameters will be interpreted slightly differently than described * parameters of the pa_buffer_attr structure will be interpreted
* above when passed to pa_stream_connect_record() and * slightly differently than otherwise when passed to
* pa_stream_connect_playback(): the overall latency that is comprised * pa_stream_connect_record() and pa_stream_connect_playback(): the
* of both the server side playback buffer length, the hardware * overall latency that is comprised of both the server side playback
* playback buffer length and additional latencies will be adjusted in * buffer length, the hardware playback buffer length and additional
* a way that it matches tlength resp. fragsize. Set * latencies will be adjusted in a way that it matches tlength resp.
* PA_STREAM_ADJUST_LATENCY if you want to control the overall * fragsize. Set PA_STREAM_ADJUST_LATENCY if you want to control the
* playback latency for your stream. Unset it if you want to control * overall playback latency for your stream. Unset it if you want to
* only the latency induced by the server-side, rewritable playback * control only the latency induced by the server-side, rewritable
* buffer. The server will try to fulfill the client's latency requests * playback buffer. The server will try to fulfill the client's latency
* as good as possible. However if the underlying hardware cannot * requests as good as possible. However if the underlying hardware cannot
* change the hardware buffer length or only in a limited range, the * change the hardware buffer length or only in a limited range, the
* actually resulting latency might be different from what the client * actually resulting latency might be different from what the client
* requested. Thus, for synchronization clients always need to check * requested. Thus, for synchronization clients always need to check
@ -164,8 +116,8 @@
* tlength/fragsize, regardless whether PA_STREAM_ADJUST_LATENCY is * tlength/fragsize, regardless whether PA_STREAM_ADJUST_LATENCY is
* set or not. * set or not.
* *
* The server-side per-stream playback buffers are indexed by a write and a read * The server-side per-stream playback buffers are indexed by a write and
* index. The application writes to the write index and the sound * a read index. The application writes to the write index and the sound
* device reads from the read index. The read index is increased * device reads from the read index. The read index is increased
* monotonically, while the write index may be freely controlled by * monotonically, while the write index may be freely controlled by
* the application. Subtracting the read index from the write index * the application. Subtracting the read index from the write index