[mythtv] How to report a reproducible mythfrontend crash on a particular video segment

[Derek Atkins]

Taco Mel <taco_mel at yahoo.com> writes:

> Hello.  I made a recording yesterday that causes a
> reproducible crash of mythfrontend at the exact same
> place every time.  I see a ticket on this in "trac"
> but the reporter is having a hard time reproducing it.
>  So I'd like to be able to add my experience as a data
> point since I can reproduce this with my recording.
>
> My question is, would it be valuable to provide the
> exact video that is causing the problem?  If so, is
> there a way to "clip" out a certain segment, because
> the recording is 34 GB (a college football game
> recorded in HD).  I'm happy to use either MythTV
> itself or some other command line tool but would need
> a hint to get started.  (The recording is in MPEG
> format from a pcHDTV 5500.)
>
> Please advise on the best way to report this crash. 
> Thanks in advance.

What I do is the following:

1) Watch the video and set the "watch point marker" a few seconds
   before the fatal error

2) enter mysql and search the recorded table for the exact chanid and
   start time of your episode.  e.g. for letterman:

   select * from recorded where title='late show with david letterman';

3) search the recordedmarkup table to find the watch point for the
   particular episode.  e.g.:

   select * from recordedmarkup where chanid=2931 and 
     starttime='2007-08-27 23:34:00' limit 10;

4) search the recordedseek table to find the actual file offsets around
   where your mark is.  e.g., if your mark was 100125 you could use
   something like:

   select * from recordedseek where chanid=2931 and 
     starttime='2007-08-27 23:34:00' and mark > 100083 and mark < 100200;

   note that you need to use a range because your recordedmarkup point
   might not be an exact recordedseek entry.  Just find one close to
   where you want to be.

5) use the actual offset to slice up your datafile.  e.g. if the closest
   offset to 100125 was at byte 7387911012, run:

   tail --bytes=+7387911012 /mythtv0/video/2931_20070827233400.mpg | \
     head -c 44916560 > /tmp/test-case.mpg

   This will give you an ~40MB testcase.

6) upload your testcase to a server where some developer can pull it
   down.  Feel free to test this clip with 'mythtv' on your own first
   to verify that it contains the bad frame(s).

Enjoy!

-derek

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord at MIT.EDU                        PGP key available