[mythtv-users] HDHomerun and previews (crashes backend)

Michael Tiller michael.tiller at gmail.com
Thu Jan 25 22:27:58 UTC 2007

I've got an HDHomerun and while I'm generally happy with it, it is giving me
some grief.  I don't really know whether I should report this to the
HDHomerun guys or the Myth mailing list of the FFMPEG mailing list.  Let me
describe the issue and perhaps people here can comment.

My problem is with thumbnail generation.  The FFMPEG code is generally not
very robust to garbage data structures.  As a result, it will divide by
zero, dereference null pointers, etc.  Where does the garbage come from?
Well it consistently comes from my HDHomerun.  This is a bit odd since I'm
capturing from QAM and my signal strengths all seem quite reasonable.  So it
is not a reception problem and I'm assuming its not a lock problem.  But
nevertheless when FFMPEG tries to generate previous it crashes the backend
(at this point it is always a segfault but sometimes it comes directly from
the FFMPEG code and sometimes it comes from free/malloc due, presumably, to
a corrupte malloc heap or something).

I've tried to apply some simple patches but I really don't know enough about
how FFMPEG works to figure out what the "right" thing to do is.  It seems
like FFMPEG seems to be built around the idea that it always gets valid data
because there doesn't seem to be much infrastructure for handling return
codes and trapping errors.

But is making FFMPEG bullet proof the real solution?  Is there a way to get
a valid data stream.  Afterall, it seems like it is tuning and locking ok so
how is the data going bad?  Is the "corruption" of the video an HDHomerun
issue or a MythTV issue...hard for me to know where to even start in
figuring that out.

Is anybody else having similar problems?  At what level is it best to attack
this problem?!?

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