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This shows you the differences between two versions of the page.

--- tutorial:writing_your_own_filter [2010/04/14 00:29]
j.m Period.
+++ tutorial:writing_your_own_filter [2012/11/11 08:51]
@@ Line 1: / Line 1: @@
-====== Writing your own filter ======
-This page tries to explain how to write your own filter.
-===== Setup & tools =====
-First of all you need Avidemux sources (if you do plugins you don't even have to compile Avidemux itself but you still need the sources).
-For windows, you need MinGW GCC/g++ (v4.x) or cygwin GCC/g++ (v4.x).
-MSVC will not work as there will be some C++ links and MSVC C++ is incompatible with g++.
-===== Everything is a class =====
-All filters inside Avidemux are derivative of AVDMGenericVideoStream class.
-Only a few methods need to be defined:
-===== The constructor =====
-It takes 2 arguments:
-  - The previous filter in the chain, it will be copied into _in
-  - CONFcouple * couples which contains the configuration. It it is null it means you have to use your default value.
-The constructor has to update its _info field which contains a description of the output format.
-If you dont change fps nor width/height you can just copy the one from the previous filter using _in<nowiki>-></nowiki>getInfo().
-You should have a field of your class named _param which is a structure describing your parameters.
-For example:
-<code cpp>
-typedef struct rotateParam
- {
-   uint32_t angle;
- }rotateParam;
-</code>
-In the constructor you can use the handy *GET* macro to retrive the parameter from CONFcouple
-e.g. GET(angle);
-===== printConf =====
-The next method is printConf. It is used to print the configuration in the filter dialog box.
-<code cpp>
-char *yourClassName::printConf (void)
-{
-  static char buf[[50]];
-  sprintf ((char *) buf, " My rotate filter, angle :%d",_param->angle);
-  return buf;
-}
-</code>
-Note that the buffer is static to avoid allocating/freeing it as it can be complicated.
-===== GetCouple =====
-This method is used to retrieve the current configuration. The simplest way is to use the CSET macro like this:
-<code cpp>
-uint8_t yourClassName::getCoupledConf (CONFcouple ** couples)
-{
-  ADM_assert (_param);
-  *couples = new CONFcouple (1); // Number of param in your structure
-  #undef CSET
-  #define CSET(x)  (*couples)->setCouple(#x,(_param->x))
-  CSET (angle);
-  return 1;
-}
-</code>
-getCoupledConf and the constructor are a pair. It is vital they use the same number of parameters and the same parameter names. Else you will have asserts popping.
-===== Configure =====
-<code cpp>uint8_t yourClassName::configure (AVDMGenericVideoStream * in)</code>
-This method is used to configure the filter. The parameter is the same as for the constructor. It is safer to update _in with it though.
-It is recommended (strongly) to use dialogFactory as it will work on both GTK+ and Windows (Qt) and is quite simple to use.
-Some info:
-  * Returning 0 means nothing has changed.
-  * Returning 1 means you have changes something and that the filter chain might have to be rebuild.
-**Important**: The change must be done immediately in configure!
-===== getFrameNoAlloc =====
-This is the central method as the work will be done here.
-<code cpp>
-uint8_t yourClassName::getFrameNumberNoAlloc (uint32_t inframe,
-                              uint32_t * len,
-                              ADMImage * data, uint32_t * flags)
-</code>
-**len** is the size in bytes of the output image.
-**flags** can be ignored.
-**inframe** is the frame you have to render.
-**data** is the place when you have to render the frame.
-Remember that the filters are a chain, so each filter may ask for (any) frame to its predecessor. In most cases you will want to allocate a temporary buffer in the constructor (which is often called _uncompressed) and ask the previous filter to fill it for you. For example, the verticalFlip can be simplified like that:
-<code cpp>
-uint8_t yourClassName::getFrameNumberNoAlloc (uint32_t inframe,
-                              uint32_t * len,
-                              ADMImage * data, uint32_t * flags)
-{
-  ADM_assert(inframe<_info.nb_frames); // Make sure we don't go out of bounds
-  // Read frames for the previous
-  ADM_assert(_in->getFrameNumberNoAlloc(inframe,len,_uncompressed,flags)); // Now _uncompressed contains the frame
-  // Flip from _uncompressed to data, which holds the final image
-  Return 1; // ok
-}
-</code>
-Some notes:
-  * All images are in YV12 format.
-  * If you need several images to render one image out (3:2 pulldown, noise removal,...), you should instantiate a VideoCache object.
-===== Declaring your filter =====
-There are 2 ways of declaring your filter: bundled or plugin. You can do both at the same time, in the same file.
-==== Bundled filter ====
-Is is a bit more complicated. You have to:
-  * Declare a tag for your filter in ADM_filter/video_filters.h
-  * Register your filter in ADM_filter/filter_declaration.cpp using
-<code cpp>
-REGISTERX("rotate","Rotate","Rotate the picture by 90, 180 or 270 degrees.",VF_ROTATE,1,rotate_create,rotate_script);
-</code>
-The first parameter is the internal name (must be unique).
-The second and 3rd parameters are the one used for display a,d brief.
-The fourth one is the tag you declared above. **DON'T REUSE AN EXISTING TAG**. You would have big problems, believe me.
-The 2 last ones must be the same as the function described below
-Let's go back to our filter C++ file.
-First you need to declare a const which looks like
-<code cpp>static FILTER_PARAM yourfilter_param =  { 1,"angle"};</code>
-The first parameter is the number of parameters in your param structure followed by the parameters name, EXACTLY like in your structure. Then use these two macros:
-<code cpp>
-BUILD_CREATE (rotate_create, yourClassName);
-SCRIPT_CREATE (rotate_script, yourClassName, yourfilter_param);
-</code>
-Make sure the first parameter of these two macros match the one you used in REGISTERX.
-That's all :-).
-==== Plugin ====
-It is simpler.
-You still have to declare the const which looks like
-<code cpp>static FILTER_PARAM yourfilter_param =  { 1,"angle"};</code>
-Then
-<code cpp>
-extern "C"
-{
-  SCRIPT_CREATE(FILTER_create_fromscript,yourClassName,yourfilter_param);
-  BUILD_CREATE(FILTER_create,yourClassName);
-  char *FILTER_getName(void)
-  {
-    return "DynRotate";  // Name of your filter. must be unique!
-  }
-  char *FILTER_getDesc(void)
-  {
-    return "Blah blah"; // Short description of your filter
-  }
-  uint32_t FILTER_getVersion(void)
-  {
-    return 1;  // Version of your filter
-  }
-  uint32_t FILTER_getAPIVersion(void)
-  {
-    return ADM_FILTER_API_VERSION;
-  }
-}
-</code>
-It is self contained, you don't have to change any file in ADM_filter/xxx if it just a plugin.
-You can do both declaration in the same file, so that it can be bundled inside Avidemux or compiled as a plugin filter.
-===== Final words =====
-The simplest it to start from the ADM_filter/ADM_vidDummyFilter.cpp which is a very simple filter you can build using
-//sh(nbsp)builddummy.sh// on Unix
-or
-//sh(nbsp)builddummy_win32.sh// on Windows (you may have to change the path/names for your gcc).
-The main differences with Avisynth are:
-  * Image format is always YV12.
-  * stride=width
-  * You don't return the frame, it is given to you by the caller as argument.

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