# D21. A GPL ffmpeg, run as a separate program (7 Oct 2026)

The desktop app and the CLI use a GPL build of ffmpeg with libx264, libwebp and zimg (on Windows and Linux the builds of BtbN/FFmpeg-Builds, which CI uses too). The core never links ffmpeg: it runs it as a separate program with command-line arguments, which the GPL FAQ treats as two programs shipped side by side, so the app keeps its own licence. Obligations for the bundled binary: its licence shown, the exact sources of that build offered, the binary replaceable. The hardware encoders (VideoToolbox, Media Foundation) stay as fallbacks only: measured on 7 Oct 2026 (Apple M5, high preset, VMAF against a lossless 1080p reference), a screen recording at 177 kb/s with libx264 CRF 21 (VMAF 96.1) takes 1,852 kb/s with VideoToolbox at the bitrate the pipeline asks (VMAF 93.4) and 2,071 kb/s at constant quality 75 (VMAF 95.5); phone footage 5.0 Mb/s (81.5) against 4.8 Mb/s (79.0), encoded 3 times faster; motion graphics 375 kb/s (91.4) against 2,046 kb/s (92.5). H.264 patents: the AVC pool licence (Via LA) is free up to 100,000 units a year for PC software, per unit above; a lawyer confirms this and the GPL reading before distribution.
H.264 stays the only codec shipped (e-learning video compresses well), with the three quality presets and `high` by default: it plays in every browser an LMS may open. AV1, measured the same day with SVT-AV1 (preset 8, as fast as libx264 `medium` on the M5), takes 35 to 55 % fewer bits at equal VMAF on filmed footage and motion graphics (3.3 instead of 5.0 Mb/s; 173 instead of 375 kb/s) and about 10 % fewer on screen recordings, but Safari plays it only on devices with an AV1 decoder (iPhone 15 Pro, M3 Macs and later). It would come as a second source next to H.264, chosen by the player through `MediaCapabilities`, which makes packages heavier and each learner's download lighter; adaptive streaming belongs to hosted courses (cloud stage).
*Revisit if:* the legal check says otherwise (then an LGPL build and screen recordings ten times heavier, or an x264 commercial licence), or when hosted delivery or LMS size limits make AV1 worth its second file.