Question regarding MathMF

Question

I want to extract images from an avi file with MathMF from https://github.com/SimonWoods/MathMF.

(please see here the answer of Simon)

A test avi file (named "20181122_test.avi") can be downloaded here: https://drive.google.com/open?id=1ek87v3mLXRHAv51jW4967vQLIO-Z-Any

Let's consider only two lines:

Line 1. Needs["MathMF"];` (to load the package)

This works and the package is loaded.

Now I want to read the number of images in the file:

Line 2. numberImages = Length@Import["20181122_test.avi", "Frames"]

That produces an error:

If I don't load the MathMF package BEFORE, then I get the correct result:

numberImages = 
 Length@Import["20181122_test.avi", "Frames"]

5

The funny thing is NOW I can again execute Needs["MathMF"]` and AFTER that I can read the number of images in the file WITHOUT error.

Can somebody reproduce the error? What is different between Mathematica 11.3 and 11.1.1 and how can I execute with Mathematica 11.3 first line 1 and then line 2 without error?

My OS is Windows 10 Pro 64 bit and I am working with Mathematica 11.3.0.0

This error does not occur with Mathematica 11.1.1

Answer 1

Judging from the error message it looks like Mathematica 11.3 is using Media Foundation (via MediaTools.dll) for the avi import (earlier versions didn't) and this is conflicting with the use of Media Foundation in my library. Most likely there is a bug in my code. I don't know C++ or COM well, so MathMF is probably not doing things quite the way they should be.

Looking at the MediaTools package it seems like it might do everything that MathMF can do anyway. If you do Needs["MediaTools`"] and then ?MediaTools`Private`$MF* there appear to be functions for frame-by-frame reading and writing.

Update

Piotr Wendykier has provided an answer here showing how to use MediaTools for frame-by-frame reading.

Answer 2

Since the error is caused by loading MathMF, so I suggest modify the MathMF package file mannually further while executing Needs["MathMF'"], in order to do this, the package main file should be modified properly.

SystemOpen@FileNameJoin[{$UserBaseDirectory, "Applications"}]

then find the MathMF.m, open it with Notepad or other text editor the content surrounded by red rectangle should be packed as a function following the package programming rules, see bellow likely

MFLoad[]:=Module[{},
    MathMFlib=FindLibrary["MathMF"];

    If[MathMFlib===$Failed,
	    Print["No MathMF.DLL found.\nMathMF will attempt to build the library from source."];
	    Module[{codefile,code},
	    codefile=FileNameJoin[ReplacePart[FileNameSplit[$InputFileName],-1->"MathMF.cpp"]];
    If[!FileExistsQ[codefile],
    Print["No source file found at "<>codefile<>"\nAborting MFMath."];Abort[]];
    code=Import[codefile,"Text"];
    Needs["CCompilerDriver`"];
    MathMFlib=CreateLibrary[code,"MathMF",
    "Language"->"C++",
    "CleanIntermediate"->True,
    "Libraries"->{"ole32.lib","mfreadwrite.lib","mfplat.lib","mfuuid.lib"}];
    If[!FileExistsQ[MathMFlib],
    Print["Library creation failed.\nAborting MFMath."];Abort[],
    Print["MathMF.DLL successfully created at "<>MathMFlib]]]];

    MFISR=LibraryFunctionLoad[MathMFlib,"InitSourceReader",{"UTF8String"},{Real,1}];
    MFGF=LibraryFunctionLoad[MathMFlib,"GrabFrame",{},{Integer,3}];
    MFSourceTime=LibraryFunctionLoad[MathMFlib,"SourceTime",{},Real];
    MFISW=LibraryFunctionLoad[MathMFlib,"InitSinkWriter",{"UTF8String",Integer,Integer,Integer,Real,Integer},"Void"];
    MFSF=LibraryFunctionLoad[MathMFlib,"SendFrame",{{Integer,3,"Constant"}},Integer];

Return[True];]

and add declaration in the usage section as

MFLoad::usage= "MFLoad[] load MathMF.dll and do preparation";

so that when Needs["MathMF'"] only loads packages functions but does not make initialization. Everytime you are going to use MathMF, you do MFLoad[] to call functions of MathMF or MFUnload[] to call the MMA meta-functions.

It's hard to use TracePrint to track the Import execution routing to find the error, so turn to MathMF author for help might be better.