Known errors - HelpSeeker/Restricted-WebM GitHub Wiki

Animated GIFs cut short when using --transparency with -p/--passes 2

I assume this is an ffmpeg or libvpx bug (haven't verified it yet). Using -pix_fmt yuva420p (needed for transparency support) during 2-pass conversion will cut the input GIF short.
-p/--passes 1 will ensure that animated GIFs have the correct length.

Wrongly analysed user filters

To determine if the user specified video and/or audio filters, the script uses the filter string in combination with stream copying and looks out for eventual failure (as FFmpeg throws an error, when trying to filter and copy streams at the same time). Based on the (non-)failure of those commands, the "raw command" during the actual conversion will either copy the input streams or pipe them in an uncompressed state (which is worse performance-wise).

These simple tests work well enough for simple filters (simple as in could be used with -af or -vf). However, as the tests use (a)nullsrc as input, special stream specifiers will also lead to failure (as the referenced streams don't exist).

Ultimately this is only a slight inconvenience, but I wanted to mention to it to avoid confusion, as the results of those tests are printed, when using the -v/--verbose flag.