For threads_hint to 1.

threads_hint sets the number of threads used in filters
for modifying the video during playback. I see at least 2
problems with that:

1. For the play pipeline, you end up with 4*number of cores threads.
   IMHO, it is not a good practice to have much more threads than
   you have cores. This is especially true for CPU bounded processing
   like what you find in the glc filters.
2. I see no synchronization to ensure that packets processed in parallel
   in a given pipeline stage are put back in the correct order in the next
   ring buffer. I have experienced playback freeze and I suspect this being
   the cause:

   In gl_play.c, you have pic_hdr->time > time + gl_play->sleep_threshold
   You end up with an underflow if this condition is true and
   pic_hdr->time < time.