Commit 9c9290f5 authored by Wim Taymans's avatar Wim Taymans

Small documentation updates and additions.

Original commit message from CVS:
* docs/design/part-qos.txt:
* gst/gstclock.c:
Small documentation updates and additions.
parent 72d0c78c
2006-03-29 Wim Taymans <wim@fluendo.com>
* docs/design/part-qos.txt:
* gst/gstclock.c:
Small documentation updates and additions.
2006-03-29 Wim Taymans <wim@fluendo.com>
* libs/gst/base/gstbasesrc.c: (gst_base_src_finalize),
......
......@@ -17,6 +17,13 @@ made:
- long term rate corrections based on trends observed in the sinks.
Sources of quality problems
---------------------------
- High CPU load
-
QoS event
---------
......@@ -38,13 +45,19 @@ Collecting statistics
A buffer with timestamp B1 arrives in the sink at time T1. The buffer
timestamp is then synchronized against the clock which yields a jitter J1
return value from the clock.
return value from the clock. The jitter J1 is simply calculated as
If the jitter is positive, the entry arrived in time and can be rendered.
J1 = B1 - CT
Where CT is the clock time when the entry arrives in the sink. This value
is calculated inside the clock when we perform gst_clock_entry_wait().
If the jitter is positive, the entry arrived in time and can be rendered
after waiting for the clock to reach time B1 (which is also CT + J1).
If the jitter is negative however, the entry arrived too late in the sink
and should therefore be dropped. A dropped buffer should generate a QoS
event upstream.
event upstream. J1 is the amount of time the entry was late.
Using the jitter we can calculate the time when the buffer arrived in the
sink:
......@@ -53,7 +66,7 @@ sink:
The time the buffer leaves the sink after synchronisation is measured as:
T2 = B1 - (J1 < 0 : J1 : 0) (2)
T2 = B1 - (J1 < 0 ? J1 : 0) (2)
For buffers that arrive in time (J1 >= 0) the buffer leaves after synchronisation
which is exactly B1. Late buffers (J1 < 0) leave the sink when they arrive,
......@@ -62,7 +75,7 @@ whithout any synchronisation, which is T1 = B1 - J1.
Using a previous T0 and a new T1, we can calculate the time it took for
upstream to generate a buffer with timestamp B1.
PT1 = T0 - T1 (3)
PT1 = T1 - T0 (3)
We call PT1 the processing time needed to generate buffer with timestamp B1.
......@@ -149,7 +162,7 @@ used as the proportion member in the QoS message that is sent upstream.
Receivers of the QoS message should permanently reduce their datarate
as given by the proportion member. Failure to do so will certainly lead to
dropped frames and worse a QoS.
more dropped frames and a generally worse QoS.
QoS strategies
......@@ -160,6 +173,7 @@ QoS strategies
- switch to a lower decoding/encoding quality
- switch to a lower quality source
QoS implementations
-------------------
......@@ -339,9 +339,10 @@ gst_clock_id_get_time (GstClockID id)
* If the @jitter argument is not NULL and this function returns #GST_CLOCK_OK
* or #GST_CLOCK_EARLY, it will contain the difference
* against the clock and the time of @id when this method was
* called. Negative values means @id was scheduled too late (and this
* function will return #GST_CLOCK_EARLY). Positive values indicate how
* early @id was scheduled.
* called. Negative values indicate how late @id was relative to the clock
* (in which case this function will return #GST_CLOCK_EARLY).
* Positive values indicate how much time was spent waiting on the clock
* before this function returned.
*
* Returns: the result of the blocking wait. #GST_CLOCK_EARLY will be returned
* if the current clock time is past the time of @id, #GST_CLOCK_OK if
......
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