Hi @ndunand,
When you say “The result is a runaway ffmpeg process that never ends, thus blocking the encoding queue”, can you please provide the log for this job? As you said, we have two fallback transcoding mechanisms in the event the lead ffmpeg binary failed to perform the transcoding: ffmpeg-aux, which is just an older version of ffmpeg and mencoder. In the event ffmpeg failed, the other two will usually fail as well but in some cases, it’s worth a try which is why it is done.
At any rate, once all three tried and failed to transcode all the pre-defined transcoding flavours in the set, the job should be marked as failed and no further attempts should be made. Need to understand why this is not happening in your case.
In regards to aborting batch jobs, see: