[FFmpeg-devel] [PATCH] AMR-WB Decoder

Justin Ruggles justin.ruggles
Sat Sep 18 17:01:23 CEST 2010

Marcelo Galv?o P?voa wrote:

> 2010/9/18 M?ns Rullg?rd <mans at mansr.com>:
>> Benjamin Larsson <banan at ludd.ltu.se> writes:
>>> On 09/18/2010 12:15 PM, M?ns Rullg?rd wrote:
>>>> Rob <robert.swain at gmail.com> writes:
>>>>> On 18 September 2010 11:43, M?ns Rullg?rd <mans at mansr.com> wrote:
>>>>>> Marcelo Galv?o P?voa <marspeoplester at gmail.com> writes:
>>>>>>> Here is my floating point AMR-WB Decoder from GSoC. The output
>>>>>>> quality seems good compared to the reference and libopencore
>>>>>>> decoders.
>>>>>> Seems good?  Does it differ by more than +-1?
>>>>> http://lists.mplayerhq.hu/pipermail/ffmpeg-soc/2010-September/009964.html
>>>> Any difference of more than 1 from the reference needs to be understood.
>>> Celp codecs usually differ more cause of more steps where differences
>>> can propagate.
>> So rounding errors are amplified?  Sounds like a bad design to me.
>> However that may be, the cause discrepancies must still be understood,
>> though not necessarily removed.  If you can explain the differences,
>> that is good enough for me.  If you do not know where they come from,
>> there could be bugs hiding.
> Well, I have not tracked the errors for analyzing propagation but I
> can tell that some parts (like the fixed gain and the fixed vector)
> differ quite a bit between the implementations. I believe the same
> applies to the existent AMR-NB decoder.
> However, in all tests I did, my decoder deviation against the source
> wav file (which was encoded by the reference encoder) was slightly
> smaller than with the reference decoder, for example:
> [...]
> The stddev when comparing both decoders is quite high I guess, but I
> should point that this decoder involves a random noise excitation
> generation for the higher frequency band, which may be part of the
> problem.

You could try doing a test using a different random generator in your
decoder and compare the 2 to see if that accounts for approximately the
same amount of difference.


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