Bug Fixes
Fixed alpha channel being destroyed during WebM optimization and conversion
Previously, optimizing or converting WebM files with transparency (alpha channel) would result in a black background replacing all transparent areas. This was caused by a chain of issues in the FFmpeg pipeline:
FFmpeg's native VP9 decoder was used by default, which silently discards the alpha channel. Now libvpx-vp9 is forced as the input decoder for WebM files with alpha.
The encoder was incorrectly set to VP8 (libvpx) instead of VP9 (libvpx-vp9). VP8 does not support alpha at all.
The -preset flag (intended for x264/x265) was being passed to VP9, which expects -speed. This could cause unpredictable encoding behavior.
Alpha detection via FFProbe was unreliable since it reports yuv420p even for files with alpha. Detection now uses the alpha_mode stream tag instead.
What this means for users: WebM files with transparency (stickers, overlays, animated graphics) now retain their alpha channel after optimization. No settings changes needed — it just works.