[FFmpeg-devel] mjpeg and llvm-gcc

[Mike Melanson]

Derk-Jan Hartman wrote:
> For VLC media player Mac OS X, we were working on using llvm-gcc for the 
> new binaries. VLC and FFmpeg was behaving very well with it, but 
> recently I noticed it crashed in ff_mjpeg_decode_sos() for almost all 
> MJPEGs.
> 
> Example file: 
> http://samples.mplayerhq.hu/V-codecs/MJPEGs/angels_480-mjpegcompress.avi
> 
> This file (and other mjpeg files) was producing "error dc" errors, and 
> eventually crashed.
> I have been able to determine that when I switch from llvm-gcc-4.2 back 
> to gcc-4.2, the crash disappeared. I have little experience trying to 
> track causes to things like this, so if anyone has any tips on how to 
> proceed, I would welcome them. If someone could try with llvm on Linux, 
> that might be useful as well. I guess this might possibly be a compiler 
> bug ? Should I try different optimization settings ?

I tried that file on a number of different configurations (including 
LLVM on Linux, both 32- and 64-bit) using this command line:

ffmpeg -idct simple -i angels_480-mjpegcompress.avi -f crc -

These were my results (troubling that there are 2 sets):

=============

There were 2 unique stdout blobs collected

The following configurations agreed on the same stdout:
   Linux / x86_32 / gcc 2.95.3
   Linux / x86_32 / gcc 3.4.6
   Linux / x86_32 / gcc 4.0.4
   Linux / x86_32 / gcc 4.3.3
   Linux / x86_32 / gcc 4.4.0
stdout:
CRC=0x45f16042


The following configurations agreed on the same stdout:
   Linux / x86_32 / llvm-svn
   Linux / x86_32 / icc 11.0
   Linux / x86_32 / icc 10.1
   Linux / x86_32 / gcc 4.1.2
   Linux / x86_32 / gcc 4.2.4
   Linux / x86_64 / llvm-svn
   Linux / x86_64 / icc 11.0
   Linux / x86_64 / icc 10.1
   Linux / x86_64 / gcc 4.0.4
   Linux / x86_64 / gcc 4.1.2
   Linux / x86_64 / gcc 4.2.4
   Linux / x86_64 / gcc 4.3.3
   Linux / x86_64 / gcc 4.4.0
   Linux / x86_64 / gcc svn
   Linux / PPC / gcc 4.0.4
   Linux / PPC / gcc 4.1.2
   Linux / PPC / gcc 4.2.4
   Linux / PPC / gcc 4.3.3
   Linux / PPC / gcc 4.4.0
   Mac OS X / x86_64 / gcc 4.0.1
stdout:
CRC=0x0e544952


-- 
     -Mike Melanson