The image JPEG encoder wrote headers and EOI without an entropy-coded scan, so its output was not a usable compressed image. The decoder's simplified inverse DCT also scaled DC incorrectly (a DC coefficient of 80 should yield 138, not a much brighter block).
Implement a standalone reusable baseline JPEG encoder with actual RGB/gray/RGBA sampling, separable vector DCT, quality-scaled quantization, Huffman/RLE coding, byte stuffing, 4:4:4 output, padded-row input, and edge replication. Wire the image format API to it with encodeWithQuality, and share an orthonormal DCT basis with a corrected inverse transform. Add a sink-based streaming Matroska/MJPEG writer using Home's existing EBML/track conventions; it preserves timestamps without retaining the recording in memory.
Validation: focused JPEG integration/encoder/DCT tests and Matroska writer tests pass in Debug and ReleaseSafe on the Home Zig toolchain; the standalone code also builds with Zig 0.15.2 in zig-camera. Independent Pillow decoding verifies generated pixels, dimensions and sampling; zig-camera CI exercises the writer on x86_64/aarch64 Linux and macOS. Full Home compiler/codec conformance was not run. This adds real MJPEG encoding, not H.264/HEVC compression support.