[mythtv-commits] Ticket #12888: Memory Alignment Bug when calling swscale

[MythTV]

#12888: Memory Alignment Bug when calling swscale
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 Reporter:  Robert Allan <rallan@…>  |          Owner:  pbennett
     Type:  Bug Report - Crash       |         Status:  assigned
 Priority:  minor                    |      Milestone:  unknown
Component:  Ports - rPi              |        Version:  0.28.0
 Severity:  medium                   |     Resolution:
 Keywords:                           |  Ticket locked:  0
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Comment (by Robert Allan <rallan@…>):

 Further investigation indicates that the bug is related to ffmpeg and its
 implementation of neon for Raspberry Pi3. A variable c->swscale is used as
 a function pointer and when this is set by the line

 SET_FF_NVX_TO_ALL_RGBX_FUNC(yuv420p, YUV420P, accurate_rnd);

 near the bottom of .../external/FFmpeg/libswscale/arm/swscale_unscaled.c,
 the bus error occurs. Commenting out this line enables previews to be
 generated but as neon optimisation has been effectively removed, live TV
 decoding is very jerky and unusable.

 Debugging further is probably too hard for me as everything is written as
 macros and then calls into 'macro'ed arm assembler code. I cannot find
 anything on web regarding this error on ffmpeg. There is a note that
 detecting arm v8 architecture is not correctly set for Pi3 but my
 understanding is that neon implementation is unaffected.

 Further background info:
 a) Raspberry Pi3 with MPEG2 license
 b) Using test command : mythpreviewgen --loglevel debug --size 0x0
 --chanid 1001 --starttime 20160430204000 --outfile
 /hdd/dvr/recordings/preview.jpg

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Ticket URL: <https://code.mythtv.org/trac/ticket/12888#comment:4>
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