[mythtv-commits] Ticket #9854: ISO playback problems

[MythTV]

#9854: ISO playback problems
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 Reporter:  Jim Stichnoth <stichnot@…>          |          Owner:  markk
     Type:  Bug Report - General                |         Status:  accepted
 Priority:  minor                               |      Milestone:  0.25
Component:  MythTV - Video Playback             |        Version:  Trunk
 Severity:  medium                              |  Head
 Keywords:                                      |     Resolution:
                                                |  Ticket locked:  0
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Comment (by Jim Stichnoth <stichnot@…>):

 Replying to [comment:5 markk]:
 > Replying to [ticket:9854 Jim Stichnoth <stichnot@…>]:
 >
 > > 2. ISOs with several titles take a long time to start up, and also to
 jump to the main menu.  See attached mythfrontend2.log output, where the
 time between 06:55:32 and 06:56:08 (36 seconds) is spent on the "Please
 Wait...." screen.
 >
 > This is a known issue that I've spent far too long trying to resolve.
 When playing back over a storage group, the libmythdvdnav object gets a
 RemoteFile object from mythtv to load the iso over the network. This uses
 a readahead thread to buffer playback but it is painfully inefficient at
 dealing with the various seeks and file checks that libmythdvdnav needs to
 do when examining the file structure etc. Blu-ray playback has a similar
 problem.
 >
 > The quick and dirty fix is to not use the readahead thread. This will
 generally reduce startup times to less than a second but you will almost
 certainly get playback issues due to the lack of buffering - especially at
 cell boundaries.
 >
 > If anyone has any other suggestions, I'm all ears.

 Mark,

 Please have a look at the mythfrontend log attached to #9864,
 http://code.mythtv.org/trac/raw-attachment/ticket/9864/mythfrontend.log.gz
 .  Besides the problem addressed in that ticket, there is evidence of
 another performance problem.  There are many bursts of successive
 mythfile_seek calls seeking to the same location.  Usually the "OPT1" case
 in FileRingBuffer::Seek() is triggered, but as soon as the readahead
 thread fills up the buffer, this optimization fails and ResetReadAhead()
 is called, and the pattern starts all over again.  I believe that if we
 could avoid resetting the readahead thread, the startup time for this ISO
 would drop from ~15 seconds down to 1-2 seconds.

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Ticket URL: <http://code.mythtv.org/trac/ticket/9854#comment:9>
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