[mythtv-users] Fast Forward with sound

[Michael T. Dean]

On 10/12/06 10:59, Sergei Gerasenko wrote:

>As for the original problem of fast-forwarding with sound, I did as you
>suggested last night by running the perl script first. It did say
>repaired/optimized for a lot of tables. Then I ran mythcommflag
>--rebuild --all and voila, everything started working like a charm.
>Thanks so much for the instructions!
>
>The only question I have now is: how do I make sure that the problem doesn't
>happen in the future? Do I need to run mythcommflag after each
>recording?
>  
>
Oh.  Forgot to mention (the thing I say in almost every post I've ever 
written that contains the word(s?) optimize_mythdb.pl) that you should 
set up a daily cron job to run optimize_mythdb.pl.  That will keep your 
tables in working order meaning that at most only one day's worth of 
recordings will have corrupt seektables (so you could run "mythcommflag 
--rebuild -f" on a specific file).

You should /not/ run "mythcommflag --rebuild" on a normal recording.  
Run it only when a recording has a broken seektable (or watch the 
recording and delete it ;).  Using "mythcommflag --rebuild" *re*builds 
the seektable that was originally built during recording.  The reason 
you had to run it on a bunch of your recordings is that you had a 
corrupt table--meaning any data stored in it since it became corrupted 
is likely broken/missing.  In these situations, it's often easier to run 
it with "--all" than to figure out which recordings are broken and fix 
only them.

>Finally, there's now this issue of seeking within a file
>that somehow has to do with mythcommflag. Is there a link to some
>article explaining all this in a little more detail? I did look through
>the documentation and couldn't find an explanation for all this. Sorry
>if this is an FAQ.
>  
>
If you want to learn for your own benefit (i.e. just to learn about how 
Myth chose to do things), the source is the best available guide to 
what's happening.  If you want to learn just so you can use a Myth box, 
you don't need to--as long as you keep your tables in working order 
(with the cron job running optimize_mythdb.pl as above), it will just work.

If your curiosity is somewhere between, here's the short answer.  
Basically, MPEG System streams don't provide seeking information within 
the data stream, so media players have to "estimate" the position in the 
stream that corresponds to the desired time to which you are attempting 
to seek.  These estimates can be /way/ off for variable bitrate streams, 
so Myth simply builds its own seektable during recording.  See also 
http://www.gossamer-threads.com/lists/mythtv/users/226752#226752 .

Mike