first stab at adding video

tests/unit/test_muxer_ffmpeg.py

@@ -0,0 +1,67 @@
+"""Unit tests for the ffmpeg muxer.
+
+Requires ``ffmpeg`` on PATH. On Windows, if ffmpeg is not installed these
+tests are skipped (they will run inside the Docker image where ffmpeg is
+always present).
+"""
+import os
+import shutil
+import struct
+
+import numpy as np
+import pytest
+
+from server.video_models.muxer import frames_and_audio_to_mp4, frames_to_mp4_loop
+
+
+pytestmark = pytest.mark.skipif(
+    shutil.which("ffmpeg") is None,
+    reason="ffmpeg not installed locally; run these inside Docker",
+)
+
+
+def _rgb_frames(t, h=64, w=64):
+    """Coloured checker frames so the encoder has real content."""
+    frames = np.zeros((t, h, w, 3), dtype=np.uint8)
+    for i in range(t):
+        frames[i, :, :, 0] = (i * 20) % 255
+        frames[i, :h // 2, :, 1] = 255
+        frames[i, :, :w // 2, 2] = 255
+    return frames
+
+
+def test_frames_to_mp4_loop_produces_mp4_bytes():
+    frames = _rgb_frames(8)
+    data = frames_to_mp4_loop(frames, fps=16)
+    assert isinstance(data, bytes)
+    assert len(data) > 0
+    # MP4 files start with an ftyp box: 4 bytes size + 'ftyp'
+    assert data[4:8] == b"ftyp"
+
+
+def test_frames_and_audio_to_mp4_produces_mp4_bytes():
+    frames = _rgb_frames(16)
+    # 1s silent audio at 24kHz
+    audio = np.zeros(24000, dtype=np.float32)
+    data = frames_and_audio_to_mp4(frames, audio, sample_rate=24000, fps=16)
+    assert isinstance(data, bytes)
+    assert len(data) > 0
+    assert data[4:8] == b"ftyp"
+
+
+def test_frames_to_mp4_loop_rejects_empty():
+    with pytest.raises(ValueError):
+        frames_to_mp4_loop(np.empty((0, 64, 64, 3), dtype=np.uint8), fps=16)
+
+
+def test_frames_and_audio_to_mp4_rejects_empty_audio():
+    frames = _rgb_frames(4)
+    with pytest.raises(ValueError):
+        frames_and_audio_to_mp4(
+            frames, np.empty(0, dtype=np.float32), sample_rate=24000, fps=16
+        )
+
+
+def test_frames_to_mp4_loop_rejects_wrong_shape():
+    with pytest.raises(ValueError):
+        frames_to_mp4_loop(np.zeros((4, 64, 64), dtype=np.uint8), fps=16)