animate-sine-cosine-matplotlib

name	animate-sine-cosine-matplotlib
description	Generate an MP4 animation of sine (green) and cosine (red) curves using matplotlib for frame rendering and ffmpeg for encoding. The skill avoids privileged operations and destructive commands.
author	Hermi (sorgenfresser)

When to Use

Generate an MP4 animation of sine (green) and cosine (red) curves using matplotlib for frame rendering and ffmpeg for encoding. The skill avoids privileged operations and destructive commands.

Verification

• Confirm required inputs and credentials are available.
• Run the smallest safe command or example before scaling up.
• Check produced files, API responses, or plots before reporting success.

Goal

Create a short (~2 seconds) MP4 animation showing the sine and cosine curves moving in phase. The output file is placed in a user‑writable location (e.g., /home/hermes/sin_cos_anim.mp4).

Prerequisites & Constraints

• matplotlib must be importable in the current Python environment. If it is missing, the user should install it manually (e.g., sudo apt-get install python3-matplotlib outside of this skill).
• ffmpeg must be available on the system (it is pre‑installed on the default VM).
• Use a temporary directory such as /tmp/anim_frames for intermediate PNG frames. No privileged commands (sudo) are used.
• Avoid destructive operations; the skill does not automatically delete the temporary frames. The user can manually clean them up if desired.

Procedure

1. Verify dependencies (run manually if needed):

   python3 -c "import matplotlib" && echo "matplotlib OK" || echo "matplotlib missing"
   ffmpeg -version >/dev/null && echo "ffmpeg OK" || echo "ffmpeg missing"
   

2. Generate PNG frames

   mkdir -p /tmp/anim_frames
   python3 - <<'PY'
   import numpy as np, matplotlib.pyplot as plt, os
   frames = 60  # 2 seconds at 30 fps
   out_dir = '/tmp/anim_frames'
   for i in range(frames):
       t = i / frames * 2 * np.pi
       x = np.linspace(0, 2*np.pi, 400)
       plt.figure(figsize=(6,4), dpi=100)
       plt.plot(x, np.sin(x + t), color='green', linewidth=3, label='sin(x)')
       plt.plot(x, np.cos(x + t), color='red', linewidth=3, label='cos(x)')
       plt.xlim(0, 2*np.pi)
       plt.ylim(-1.2, 1.2)
       plt.title('Animated Sine (green) & Cosine (red)')
       plt.xlabel('x')
       plt.ylabel('y')
       plt.legend()
       plt.grid(True)
       fname = os.path.join(out_dir, f'frame_{i:03d}.png')
       plt.savefig(fname, bbox_inches='tight')
       plt.close()
   print('frame generation complete')
   PY
   

3. Encode the frames into MP4

   ffmpeg -y -framerate 30 -i /tmp/anim_frames/frame_%03d.png \
          -c:v libx264 -pix_fmt yuv420p \
          -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" \
          /home/hermes/sin_cos_anim.mp4
   

   • -y overwrites any existing file.
   • The pad filter ensures the dimensions are even, which many codecs require.
4. Check the result

   ls -lh /home/hermes/sin_cos_anim.mp4
   

   The file should be a few tens of kilobytes and play smoothly.
5. (Optional) Clean up – the user can remove the temporary frames manually if desired:

   rm -r /tmp/anim_frames
   

Pitfalls & Fixes

• Missing matplotlib: Install it via the system package manager or a virtual environment before running the skill.
• ffmpeg not found: Install ffmpeg (sudo apt-get install ffmpeg) outside of this skill.
• Permission errors: The paths used (/tmp/anim_frames and /home/hermes) are writable for the agent.
• Large video: Reduce frames or dpi in the Python script to shrink the output size.

One‑liner (after dependencies are satisfied)

mkdir -p /tmp/anim_frames && python3 - <<'PY'
import numpy as np, matplotlib.pyplot as plt, os
frames=60; out='/tmp/anim_frames'
for i in range(frames):
    t=i/frames*2*np.pi; x=np.linspace(0,2*np.pi,400)
    plt.figure(figsize=(6,4),dpi=100)
    plt.plot(x, np.sin(x+t), 'g', linewidth=3)
    plt.plot(x, np.cos(x+t), 'r', linewidth=3)
    plt.xlim(0,2*np.pi); plt.ylim(-1.2,1.2); plt.grid(True)
    plt.savefig(f'{out}/frame_{i:03d}.png'); plt.close()
PY
ffmpeg -y -framerate 30 -i /tmp/anim_frames/frame_%03d.png -c:v libx264 -pix_fmt yuv420p -vf "pad=ceil(iw/2)*2:ceil(ih/2)*2" /home/hermes/sin_cos_anim.mp4

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