ffmpeg was shipped by jessie-backports component which has been removed this week. As such the Quibble containers based on Jessie no more have ffmpeg available and fail to build.
The jobs using those containers:
mediawiki-quibble-composer-mysql-php55-docker mediawiki-quibble-composer-postgres-php55-docker mediawiki-quibble-composer-sqlite-php55-docker mediawiki-quibble-composertest-php55-docker mediawiki-quibble-vendor-mysql-php55-docker mediawiki-quibble-vendor-postgres-php55-docker mediawiki-quibble-vendor-sqlite-php55-docker quibble-composer-mysql-php55-docker quibble-composer-mysql-php55-noselenium-docker quibble-composer-postgres-php55-docker quibble-composer-postgres-php55-noselenium-docker quibble-composer-sqlite-php55-docker quibble-composer-sqlite-php55-noselenium-docker quibble-vendor-mysql-php55-docker quibble-vendor-mysql-php55-noselenium-docker quibble-vendor-postgres-php55-docker quibble-vendor-postgres-php55-noselenium-docker quibble-vendor-sqlite-php55-docker quibble-vendor-sqlite-php55-noselenium-docker release-quibble-composer-mysql-php55-docker release-quibble-composer-postgres-php55-docker release-quibble-composer-sqlite-php55-docker release-quibble-vendor-mysql-php55-docker release-quibble-vendor-postgres-php55-docker release-quibble-vendor-sqlite-php55-docker wmf-quibble-core-vendor-mysql-php55-docker wmf-quibble-vendor-mysql-php55-docker
And
quibble-donationinterface-REL1_27-zend56-docker