Frontend crash after ffmpeg sync

[Bill <cizek@…>]

After svn 13655, mythfrontend will crash when playing recordings.

If I use ac3 pass-through it works ok; If I use myth to decode the ac3 audio, mythfrontend will crash soon after the recording starts playing or after I jump forward in the video.

I've attached a gdb backtrace and frontend log. If there's anything else I can provide please let me know.

-Bill

[elkin@…]

I can confirm that on German TV channel ProSieben, when ac3 is send the frontend decodes badly (jerky sound) or crashes the frontend. Switching to mpg2 works flawlessly

[Janne Grunau]

I can reproduce this on x86_32. x86_64 works fine.

One of our modifications to libavcodec seems to be the cause. A patched ffmpeg works fine.

[Janne Grunau]

A release build works here too.

[davidp@…]

I have the exact same problem (with the same results from gdb backtrace). When I watch certain channels (those with AC3 as well as MP2 audio streams) it crashes the frontend.

Only crashes one of my machines though, not both of them.

[Bill <cizek@…>]

I'm running x86_32 on a plain Intel Pentium 4.

A debug build has distorted audio as described in ticket 3608 and crashes very quickly.

A release build has the same distorted audio but doesn't crash.

If I use ac3 passthrough everything works ok.

[davilla@…]

Same problem here with identical segfault. Video is from a HDHomeRun recording off-the-air ATSC. There's a comment about a patched ffmpeg working fine. More details on this please as the current svn trunk is broken regarding HDHomeRuns.

[Janne Grunau]

(In [13765]) Fixes #3608. Updates ffmpeg's internal ac3 decoder

This updates the ac3 decoder in our libavcodec copy to the final patch posted on 2007-05-07 by Justin Ruggles pulls also ffmpeg revision 8816 in, since it's need by the patch. Fixes the Audio distortion reported in #3608.

Refs #3634. crashes on x86_32 with debug and release builds

[Janne Grunau]

disable the SSE imdct

[Janne Grunau]

3634_workaround.diff disables the SSE imdct in the ac3 decoder

[MaverickTech <rsmith@…>]

Replying to janne:

3634_workaround.diff disables the SSE imdct in the ac3 decoder

I applied that patch and I am not seeing the SSE crash anymore, on recordings I know to be triggering a crash. I could still readily crash the frontend prior to applying the patch.

I am currently running trunk as of yesterday (13788)

[Anduin Withers]

(In [13796]) References #3634

Force float array to align(16) for call to ff_imdct_calc_sse. The ff_imdct_calc_sse function uses movaps which will cause a GPF on unaligned data.

Another solution would be to have ff_imdct_calc_sse use movups. I'm only using the align fix as assuming correct alignment seems to be common elsewhere in there.

There may be problems with align for some versions of gcc.

[jppoet@…]

Changeset #13796 does seem to fix this problem for me, on my Core 2 Duo Fedora i386 frontend. I also tried watching a DVD using the internal player, and that is also working fine, now.

Thanks,

John

[Janne Grunau]

fixed by [13796]

[Bill <cizek@…>]

This fixed my problem.

Thanks, Bill

[cpinkham]

This ticket has been closed for a while, but as indicated it can still affect people with older (aka buggy) compilers. I've attached a 3634_workaround_v2.diff file that works around the issue a different way by moving the offending variable off the stack and into a struct that is malloc-ed. This fixes the issue on my ancient gcc v3.2.2 dev system. I'm not advocating putting this hack into SVN, I just wanted to document it in case others ran into the same issue.