I know that different encoder version do affect the encoded quality, but will the decoder/Players (includes soft and hardware) affect the decode quality?

Moreover, is there any difference when i play mp3/OGG in hardware player and the foobar?(I mean the output, without considering the function)

Thanks

As long as the decoder isn't buggy or broken they should all probably sound around the same. Probably not ABXable unless it is buggy. The differences in output are tiny rounding errors at most usually.

For Vorbis, some hardware players use a low precision mode which *does* cause audible degradations.

Result(may be inaccurate)
i use two different oggdropXPdV1.8.1 (libvorbis1.1.2, 08dec05)
and oggdropXPd V1.8.6(lancer 10 Aug 05)to decode same OGG file(read-only ticked), the wave files produced have different MD4 hash

77b9daaa87bbf61f58ed5d6aea972edf

and

3809ac0f3f29e54f6b69dcba1d5a22b7

there must be some difference!!!

I hope this post will raise the attention on decoding, it also affects the output.

The lancer builds are known to produce bit different ecodes so it is no surprise to hear that they also produce bit different decodes. However, I don't believe that anyone has been able to *hear* any differences between the encodes and I doubt that they will with the decodes, either. But, if someone knows differently I'm sure we'd all like to hear about it.

Do these decoders perform dither?

Not by default, but oggdropXPd and my oggdec both offer dithering as an option on decode.