[mythtv] Where is thumbnail generation done?

[Michael Tiller]

Nigel,

  Thanks for the hints.  I compiled the backend with debugging information
and ran it in GDB.  Sure enough, I uncovered two places where there were
problems with checking the values (one an integer that gets divided by and
another which was a pointer).  This helped me craft a basic patch to avoid
the crashes (I suspect the developers will refactor it though).

  This problem came up for me when using a HDHomerun in conjunction with SVN
MythTV.  The stack trace and patch are available here:
http://svn.mythtv.org/trac/ticket/2889.

  Thanks again for the tips.  It motivated me to learn how to debug MythTV
which hopefully will help me provide better clues to developers for any
future problems I have.

--
Mike

On 1/7/07, Nigel Pearson <nigel at ind.tansu.com.au> wrote:
>
>         Sorry for the delay in replying.
>
>
> 1) Crashing should always be investigated with a debugger
> (e.g. gdb). There is a section in the doco to help you.
> (although recompiling with debug can take a while)
>
>
>
> > Can anybody give me a hint about how thumbnails are generated?
>
>         Not much, but a quick search reveals:
>
> % find . -name \*.cpp -exec egrep -i thumb {} \; -print
>    *ptr++ = 0x00; *ptr++ = 0x00; // no thumbnail
> ./libs/libmythlivemedia/liveMedia/JPEGVideoRTPSource.cpp
>      /* Delete preview thumbnail. */
> ./programs/mythbackend/mainserver.cpp
>      // Add Thumbnail Resource
> ./programs/mythbackend/upnpcdstv.cpp
>      gc->setLabel(QObject::tr("Display thumbnail preview images of "
>      bs->setLabel(QObject::tr("Time offset for thumbnail preview
> images"));
>                      "thumbnail image this many seconds from the
> beginning "
>                      "as the offset for creating a thumbnail image. "
> ./programs/mythfrontend/globalsettings.cpp
>
>
>         s/thumb/Preview Image/:
>
> % find . -name \*.cpp -exec egrep -i 'preview.*image' {} \; -print
> *  \brief This class creates a preview image of a recording.
> ./libs/libmythtv/previewgenerator.cpp
>      if (sURI == "getPreviewImage"      ) return( HSM_GetPreviewImage );
>                  case HSM_GetPreviewImage: GetPreviewImage
> ( pRequest ); return( true );
> void HttpStatus::GetPreviewImage( HTTPRequest *pRequest )
>      // check to see if preview image is already created.
>          // Must generate Preview Image
>          // Generate Preview Image and save.
> ./programs/mythbackend/httpstatus.cpp
>                  "find file locally, unable to make preview image.");
>          VERBOSE(VB_IMPORTANT, "MainServer: Failed to make preview
> image.");
> ./programs/mythbackend/mainserver.cpp
>      sURI = QString( "%1getPreviewImage%2").arg( sURIBase   )
> ./programs/mythbackend/upnpcdstv.cpp
>      gc->setLabel(QObject::tr("Display thumbnail preview images of "
>      bs->setLabel(QObject::tr("Time offset for thumbnail preview
> images"));
>      gc->setLabel(QObject::tr("Generate preview image from a bookmark "
>          QImage* previewImage = new QImage(preview.absFilePath());
>          if (previewImage->width() == 0 || previewImage->height() ==
> 0) {
>              cout << QObject::tr("Problem reading theme preview image ")
>          addImageSelection(theme->fileName(), previewImage);
> ./programs/mythfrontend/globalsettings.cpp
>        // Preview Image Variables
>              previewPixmap->convertFromImage(tmp2);
>              previewPixmap->convertFromImage(*image);
> ./programs/mythfrontend/playbackbox.cpp
>
> %
>
>
> 2) Have a look in libs/libmythtv/previewgenerator.cpp,
> or programs/mythbackend/mainserver.cpp ?
> Just compiling those with debug symbols should be
> enough to get more useful output from gdb
>
>
>
> Good luck!
>
> --
> Nigel Pearson, nigel at ind.tansu.com.au|"Beware - I am a carrier
> Telstra Net. Eng., Sydney, Australia |          of surrealism"
> Office: 9202 3900    Fax:  9261 3912 |       D  A
> Mobile: 0408 664435  Home: 9792 6998 |       L  I
>
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