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--- wiki:statmux_priorities [2016/12/09 09:07] – [Specifications] walkeradmin
+++ wiki:statmux_priorities [2023/03/09 22:35] (current) – external edit 127.0.0.1
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 ==== Context ====
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+----
 ==== Specifications ====
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 In this first version, the priority will be set only by mpeg4.cfg by specifying for each channel the prioritized level (1 or 0), using  the following line:
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 {{:wiki:statmuxpriorities01.png?500|}}
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+To set a priority to this channel:
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+<color red>Service1.Profile 1-1.vid0.statmuxPriority=1</color>
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+By default, all channels will set to un-prioritized.
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+The expected behaviour is that a prioritized channel will have a better average objective video quality than without being prioritized. It could be checked by comparing in the same pool the same channel with and without priority.
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+The improved VQ will be achieved by allocating more bitrate to prioritized channels compared to others. However, a prioritized channel could have in particular cases, a lower bitrate and so a lower VQ compared to non-prioritized channel.
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+The maximal increase of bitrate, i.e. by comparing a channel bitrate with a VERY HIGH PRIORITY and the same channel with a normal priority, could be changed by mpeg4.cfg using the following parameter:
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+<color red>statmux.m_smxPriorityRateFactor=0.5.</color>
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+The default value is 0.2. The overridden value is clipped between 0.05 and 1.
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+----
+==== 3	Priorities design ====
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+Five priority levels have been planned. However, in the current state, only two priorities are used (VERY_HIGH and NORMAL):
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+  * 	SMX_PRIORITY_VERY_HIGH		= 5
+  * 	SMX_PRIORITY_HIGH		= 4
+  * 	SMX_PRIORITY_NORMAL		= 3
+  * 	SMX_PRIORITY_LOW		= 2
+  * 	SMX_PRIORITY_VERY_LOW		= 1
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+According to the maximal increase of bitrate  , priorities factor are:
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+{{:wiki:statmuxpriorities02.png?500|}}
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+Once the priority factor is computed, the statmux algorithm weights the complexity (STC) with each priority in order to balance the channel bit rate. Priorities are computed each time a channel is added or removed from the pool.
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+----
+==== 4	Priorities and distortion control ====
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+The distortion control aims at weighting channel’s complexity according to their MSE. Bigger the channel’s MSE, bigger the distortion factor is. Factors are computed every four statmux iterations (around twice a second). Factors are clipped between 0.5 and 2.
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+However, when priorities are enabled, the distortion control could in some cases nullify the priority.  Indeed, as distortion factors can inferior to 1, it could nullify the impact of prioritizing a channel.
+To avoid such cases, factors are clipped according to the channel’s complexity:
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+  * 	1.00 < F < 2.0 with a very high priority
+  * 	0.75 < F < 2.0 with a high complexity
+  * 	0.50 < F < 2.0 with a normal priority
+  * 	0.50 < F < 1.5 with a low priority
+  * 	0.50 < F < 1.0 with a very low complexity.
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