Ghosts S01e11 Libvpx -

Ghosts in the Machine: Debugging FFmpeg’s Libvpx Encoder (Season 1, Episode 11)

The blocks don’t look like corruption. They look like... memories. Shadows of a previous frame refusing to leave. You’ve just encoded a 10-bit source with Libvpx (VP9), and somehow, the ghost of frame 1,042 is haunting frame 1,043. ghosts s01e11 libvpx

# Check your version ffmpeg -version | grep libvpx # If it's 1.11 or 1.12, upgrade. If you can’t upgrade (e.g., in a production container), tune around the bug by reducing the temporal dependency depth. Ghosts in the Machine: Debugging FFmpeg’s Libvpx Encoder

The ghosting bug in Libvpx v1.11.0–v1.12.0 is largely fixed in v1.13.0+. The patch (Change-Id: I8a3f7b2e9c4d1a5f6e7b8c9d0e1f2a3b4c5d6e7f) corrects the reference frame buffer reset logic after scene detection. Shadows of a previous frame refusing to leave

ffmpeg -i input.mov -c:v libvpx-vp9 \ -tile-columns 2 -row-mt 1 \ -lag-in-frames 16 \ # Reduce from default 25 -auto-alt-ref 1 \ # Keep on, but be careful -arnr-maxframes 3 \ # Reduce temporal filtering -cpu-used 2 \ output.webm Two-pass encoding often masks the bug because the first pass forces the encoder to re-evaluate scene boundaries more strictly.

# Disable alt-ref and limit reference frames ffmpeg -i input.mov -c:v libvpx-vp9 -auto-alt-ref 0 -arnr-maxframes 0 -lag-in-frames 0 output.webm If the ghost disappears, you’ve confirmed it’s an ALTREF or Golden Frame issue. You have three solutions, ranked from "quick fix" to "proper patch."

Drop your Libvpx war stories in the comments below.