[FFmpeg-devel] [PATCH] ac3_parser type punning fix
Mon Oct 20 10:40:48 CEST 2008
On Oct 19, 2008, at 2:31 PM, Michael Niedermayer <michaelni at gmx.at>
> On Sun, Oct 19, 2008 at 12:26:31PM -0700, Baptiste Coudurier wrote:
>> Hi guys,
>> Michael Niedermayer wrote:
>>> On Sun, Oct 19, 2008 at 05:23:52PM +0100, M?ns Rullg?rd wrote:
>>>> Michael Niedermayer <michaelni at gmx.at> writes:
>>>> Looking at the code, I see one significant difference between
>>>> aac_sync() and ac3_sync(). Whereas aac_sync() only calls inlined
>>>> get_bits() functions (meaning gcc can know exactly what accesses
>>>> happening), ac3_sync() calls another function to do the parsing.
>>>> light of this, I agree it's unlikely that gcc is able to exploit
>>>> aliasing tricks. The disassembly above also suggests that
>>>> more sinister is afoot here.
>>>> The change to aac_sync() fixed a real aliasing violation, and I
>>>> verified the assembler before and after the change. This seems
>>>> to be
>>>> a bit different.
>> FYI, Mans and I talked about this issue some time ago, and then I
>> a roundup issue regarding this (raw aac playback is broken)
> i cant find that issue, do you maybe know its number or a search
> term that
Yes, it is issue 527, my memory fails a bit, I only confirmed the issue.
>> Even at r15647 raw aac is still borken because the parser is still
> i dont know about the parser but raw aac is broken because
> the aac decoder does
> if (avccontext->extradata_size <= 0 ||
> decode_audio_specific_config(ac, avccontext->extradata,
> return -1;
> and nothing in raw.c nor in the parser sets extradata, nor is there a
> AVCodecParser.split() that would cause extradata to be set.
> Thats also why aac in mpeg-ts does not work ...
Well It is broken since some time now ... before aac decoder, and
still broken with faad which supports both bitstream formats.
Btw, I guess these (aac, ac3) parsers should be updated when state64
will be added, needed by the dnxhd parser which I will commit soon (like
Baptiste COUDURIER GnuPG Key Id: 0x5C1ABAAA
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