This is a regression introduced by 39e3d00:

thread 'decoder::stateless::h264::vaapi::tests::test_25fps_block' panicked at 'called `Result::unwrap()` on an `Err` value: decoder error: decoder error: while syncing picture

The sync() call on submit_picture when in blocking mode causes an internal decoder error on the VAAPI side. This doesn't happen in non-blocking mode, and also doesn't happen prior to commit 39e3d00. The AMD driver also seems to be unaffected.

Guess the first thing to do would be to set LIBVA_TRACE and check whether the sequence of calls to libva before and after this CL is different - it should not, but obviously something has changed.