VMD files are primarily used to record character movements, camera trajectories, and other animation information. This article will provide a detailed overview of the structure and usage of VMD files.

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File Structure

A VMD file is a binary stream file that contains multiple sections:

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Keyframe Record Details

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Bone Keyframe Record

struct BoneKeyFrame {
  char BoneName[15];     // Bone name (ShiftJIS encoding)
  uint32_t FrameTime;    // Keyframe time
  float Translation[3];  // Position coordinates (X, Y, Z)
  float Rotation[4];     // Rotation quaternion (X, Y, Z, W)
  uint8_t Curve[64];     // Curve data for X, Y, Z directions (16 bytes each)
};

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Morph Keyframe Record

struct MorphKeyFrame {
  char MorphName[15];    // Morph name (ShiftJIS encoding)
  uint32_t FrameTime;    // Keyframe time
  float Weight;          // Weight value
};
The structures for camera and light keyframes are similar but contain their specific parameters.

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Usage and Compatibility

VMD files are typically used in conjunction with MikuMikuDance software, supporting the import and export of motion data between different models.
Due to the possibility of different skeletal structures in various models, it is essential to ensure compatibility between the model and the motion data when using VMD files to avoid unnatural animation effects.

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Conclusion

The VMD file format is an indispensable part of MMD animation production. By accurately recording various parameters in animations, it allows users to create smooth and expressive animations. Understanding its structure and usage is crucial for producing high-quality MMD animations.

Learn More

Visit the MMD Wiki for more information about the VMD file format.