[FFmpeg-devel] AMR-NB decoder
Wed Aug 5 21:28:25 CEST 2009
Colin McQuillan wrote:
> 2009/8/5 Vitor Sessak <vitor1001 at gmail.com>:
>> Colin McQuillan wrote:
>>> 2009/8/5 Vitor Sessak <vitor1001 at gmail.com>:
>>>> Hi, and good work!
>>>> Colin McQuillan wrote:
>>>>> Attached is a patch for an AMR-NB decoder.
>>>>> It is not bit-exact.
>>>> Neither it could be, it is float-based. The best you could get would be a
>>>> stddev of ~0.05.
>>>>> This makes it tricky to verify, but I have been
>>>>> checking that internal parameters match the 3GPP decoder for the AMR
>>>>> test sequences. The PSNR between the input and output is 3.90 to 8.42
>>>>> which is about the same as the reference decoder.
>>>> I suppose here you mean the stddev, not the PSNR. Also, what command are
>>>> using to compare the results? Are you setting elem_size to 2? Could you
>>>> paste the output of tiny_psnr for the test vectors (and a real-world
>>> I forgot to add elem_size to my tiny_psnr script. PSNR is now actually
>>> between 20 and 80. (and from encoder input, the PSNR is about 20 to
>>> samples/A-codecs/amr/sample.amr compared against ref decoder output:
>>> stddev: 24.22 PSNR: 68.63 bytes: 797760/ 797760
>>> The test vector tiny_psnr output is attached because there's 169 of them.
>>> soc/T_102/T00_102.raw: stddev: 55.89 PSNR: 61.37 bytes: 90560/
>>> soc/T_102/T01_102.raw: stddev: 5283.25 PSNR: 21.86 bytes: 90560/
>>> soc/T_102/T02_102.raw: stddev: 999.99 PSNR: 36.32 bytes: 128000/
>>> soc/T_102/T03_102.raw: stddev: 3327.29 PSNR: 25.88 bytes: 128000/
>>> soc/T_102/T04_102.raw: stddev: 228.36 PSNR: 49.15 bytes: 95680/
>>> soc/T_102/T05_102.raw: stddev: 248.60 PSNR: 48.41 bytes: 71040/
>>> soc/T_102/T06_102.raw: stddev: 65.63 PSNR: 59.98 bytes: 106560/
>>> soc/T_102/T07_102.raw: stddev: 72.93 PSNR: 59.06 bytes: 115520/
>>> soc/T_102/T08_102.raw: stddev: 1831.37 PSNR: 31.06 bytes: 108160/
>>> soc/T_102/T09_102.raw: stddev: 47.08 PSNR: 62.86 bytes: 129600/
>> Wow, that's a pretty variated bunch. It really gives an impression that
>> there is some feature that is not properly decoded (an psnr of 22 is pretty
>> low). Does the output of T01_102.raw sounds the same as the ref decoder?
> T01_102.raw was different, I made a mistake with how I clip samples
> and didn't rerun the tests. After reverting this change, the psnr's
> are as attached.
> The T02/T03 tests still have a high PSNR but do sound the same as the
> ref decoder. T02/T03 are pure tones going from low to high. A pure
> tone will be encoded in AMR (or any CELP codec) using feedback. This
> explains why the floating-point decoder differs so much from the ref
> output - errors can accumulate.
One way to see if this is true is to compare the original (pre-encoding)
data with the decoded file by both decoders. If it is just an
arbitrary rounding that accumulates, ffamr should perform better than
ref in about 50% of the files.
> The internal parameters are all very
> close to the reference decoder. Unfortunately I don't know how to test
> the output to show whether it's just a difference in phase.
Maybe plotting both outputs with gnuplot?
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