Justification: fails to build from source (but built successfully in the past)
Hi. While we appreciate that you took the time to write a detailed bug report, this is not a "fails to build from source" bug in the usual sense. Apparently, you took the Debian source and made some modifications:
Rules: changed --prefix=/usr/local removed --enable-libbluray removed --enable-libcdio removed --enable-libjack added --disable-doc
If you do that, you are responsible for whatever build failure that you might get. In particular, the error you get seems to be correlated with the --disable-doc that you added:
# Create index.html page for the FFmpeg manual cd debian/tmp/usr/share/doc/ffmpeg && tree -H '.' -L 1 -P '*.html' --noreport --charset utf-8 -T 'FFmpeg Manual Index' -o index.html /bin/sh: 1: cd: can't cd to debian/tmp/usr/share/doc/ffmpeg
Debian can only ensure that packages build from source for the Debian source package that we provide, not for any random alteration that you could make. Additionally, we support building with some variations when using the DEB_BUILD_OPTIONS environment variable. For example, had this package supported the "nodoc" option, and had you tried to use such option, this would be indeed a bug (but not serious). Also, for trixie and above, if you get a build failure using "nocheck", that would be serious. Thanks.