AviSynth Syntax - 2.6 Multithreading and memory functions

A historical page showing how memory settings and multithreading for classic Avisynth 2.6 worked.

SetMemoryMax

SetMemoryMax(amount)

Sets the maximum memory (in MB) that AviSynth uses for its internal Video Frame cache to the value of amount. From v2.5.8, setting to zero just returns the current Memory Max value. In the 2.5 series the default Memory Max value is 25% of the free physical memory, with a minimum of 16MB. From rev 2.5.8 RC4, the default Memory Max is also limited to 512MB.

Free	<64	128	256	512	1024	2048	3072
Default Max v2.57 and older	16	32	64	128	256	512	768
Default Max since v2.58 RC4	16	32	64	128	256	512	512

In some versions there is a default setting of 5MB, which is quite low. If you encounter problems (e.g. low speed) try to set this values to at least 32MB. Too high values can result in crashes because of 2GB address space limit. Return value: Actual MemoryMax value set.

Examples:

SetMemoryMax(128)

GetMTMode, SetMTMode

GetMTMode(threads)
SetMTMode(mode, threads)

These functions enable AviSynth to use more than one thread when processing filters. This is useful if you have more than one cpu/core or hyperthreading. This feature is still experimental.

GetMTMode(bool threads):

If threads is set to true GetMTMode returns the number of threads used else the current mode is returned (see below). Default value false.

SetMTMode(int mode, int threads):

Place this at the first line in the avs file to enable temporal (that is more than one frame is processed at the same time) multithreading. Use it later in the script to change the mode for the filters below it.

mode: There are 6 modes 1 to 6. Default value 2.

• Mode 1 is the fastest but only works with a few filter.

• Mode 2 should work with most filters but uses more memory.

• Mode 3 should work with some of the filters that doesn't work with mode 2 but is slower.

• Mode 4 is a combination of mode 2 and 3 and should work with even more filter but is both slower and uses more memory

• Mode 5 is slowest but should work with all filters that doesn't require linear frameserving (that is the frames come in order (frame 0,1,2 ... last).

• Mode 6 is a modified mode 5 that might be slightly faster.

threads: Number of threads to use. Set to 0 to set it to the number of processors available. It is not possible to change the number of threads other than in the first SetMTMode. Default value 0.

Example:

SetMTMode(2,0)                      # enables multithreading using thread = to
                                    # the number of available processors and mode 2
LoadPlugin("...\LoadPluginEX.dll")  # needed to load avisynth 2.0 plugins
LoadPlugin("...\DustV5.dll")        # Loads Pixiedust
Import("limitedsharpen.avs")
src = AviSource("test.avi")
SetMTMode(5)                        # change the mode to 5 for the lines below
src = src.ConvertToYUY2.PixieDust() # Pixiedust needs mode 5 to function.
SetMTMode(2)                        # change the mode back to 2
src.LimitedSharpen()                # because LimitedSharpen works well with mode 2
# display mode and number of threads in use
Subtitle("Number of threads used: " + String(GetMTMode(true))
 \ + " Current MT Mode: " + String(GetMTMode()))

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$Date: 2024/01/06 20:02:00 $