UMC: MPEG2 Decoder Crash

[Scott_Danahy]

Hi,

I've encountered a case where the MPEG2 decoder crashes. I havenumThreads set to 8 and there appears to be a problem correctly setting up the internal worker threads. One of theMPEG2VideoDecoderBase::ThreadWorkingRoutine instances will callDecodeSlices with null buffer pointers (IppVideoContext::bs_* values are all NULL or zero).

This seems to happen whenm_nNumberOfThreads andcurr_thread do not match after the thread initialization loop inMPEG2VideoDecoderBase::DecodePicture.

I can reproduce this with simple_player like this:

simple_player.exeD:\\crash.m2v -vnul -t 8

This only happens for certain MPEG2 bistreams. Has anyone else seen this issue? Any suggestions on how to work around it?

Scott

[Alexander_Modenov__I]

Hi Scott,

You wrote "This fixdoesn'tmake a lot of sense to me". But I see no artifacts on streams provided by you.

Do you have another streams with artifacts ?

Please send it.

PS

The behaviour ofSHOW_HI9BITS is incorrect for chrominance blocks with dct_dc_size=11. Additional bit required to get correct data from theMPEG2_DCSIZE_TAB.

Regards,

Alexander

[Scott_Danahy]

Hi Alexander,

Thank you for explaining the problem, and no I don't see anyadditionalproblems. Are there any cases other than chroma blocks with dct_dcsize=11 where SHOW_HI9BITS needs to load additional bits? I'm just trying to make sure I understand. :)

Thanks for all your effort!

Scott

[Alexander_Modenov__I]

Hi Scott,

The SHOW_HI9BITS macro needs to load additional bit (only one) in very special case - when internal bit offset is 7 and the dct_dc_size for chroma block is 11 (and 10 to be honest). No such problem for limunance blocks because according to standard dct_sc_size sizes table for luminance uses maximum 9 bits per length and chroma dct_dc_size table uses maximum 10 bits. I've added simple and easy modification to SHOW_HI9BITS for all the cases for unity.

This change doesn't affect performance and codec stability I think.

Regards,

Alexander

PS

If you find any problems you are always welcome.

[Scott_Danahy]

Hi Alexander,

Thanks for taking the time to explain. Iappreciateyour efforts inresolvingthis. So far our batch testing looks great.

Scott

[Chao_Y_Intel]

Hi Scott,

The fix suggested by Alexander is also included in the 7.0.2 release.

Regards,
Chao