[mythtv-commits] Ticket #1079: frame corruption in preview playbackbox

[MythTV]

#1079: frame corruption in preview playbackbox
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 Reporter:  jwestfall at surrealistic.net  |        Owner:  ijr     
     Type:  defect                      |       Status:  reopened
 Priority:  minor                       |    Milestone:  0.20    
Component:  mythtv                      |      Version:  head    
 Severity:  low                         |   Resolution:          
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Changes (by jwestfall at surrealistic.net):

  * resolution:  worksforme =>
  * status:  closed => reopened

Comment:

 The issue is with the video preview not the static pixmap.  The code in
 PlaybackBox::updateVideo is doing

 {{{
        VideoFrame *frame = nvp->GetCurrentFrame(w, h);

         if (w == 0 || h == 0 || !frame || !(frame->buf))
         {
             nvp->ReleaseCurrentFrame(frame);
             return;
         }

         unsigned char *yuv_buf = frame->buf;
         if (conv_rgba_size.width() != w || conv_rgba_size.height() != h)
         {
             if (conv_rgba_buf)
                 delete [] conv_rgba_buf;
             conv_rgba_buf = new unsigned char[w * h * 4];
             conv_rgba_size = QSize(w, h);
         }

         conv_yuv2rgba(conv_rgba_buf,
                       yuv_buf, yuv_buf + (w * h), yuv_buf + (w * h * 5 /
 4),
                       w, h, w * 4, w, w / 2, 0);

         nvp->ReleaseCurrentFrame(frame);

         QImage img(conv_rgba_buf, w, h, 32, NULL, 65536 * 65536,
                    QImage::LittleEndian);
         img = img.scale(videoRect.width(), videoRect.height());

         p->drawImage(videoRect.x(), videoRect.y(), img);
     }
 }}}

 for each frame to be displayed in the preview video box.  There is no
 locking on the frame and frame->buf is being passed to conv_yuv2rgba().
 This leaves the decoder thread open to overwrite frame->buf while its
 being processed by yuv2rgba().  It may not be noticeable in the mmx
 version of yuv2rgba(), but you can definitely see the issue in the c
 version which is ultra slow.

-- 
Ticket URL: <http://svn.mythtv.org/trac/ticket/1079>
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