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

[Marcelo Galvão Póvoa]

On 9 September 2010 05:11, Vitor Sessak <vitor1001 at gmail.com> wrote:
> On 09/09/2010 02:50 AM, Marcelo Galvão Póvoa wrote:
>>
>> On 8 September 2010 06:54, Vitor Sessak<vitor1001 at gmail.com>  wrote:
>>>
>>> On 09/07/2010 03:21 AM, Marcelo Galvão Póvoa wrote:
>>>>
>>>> Hello,
>>>>
>>>> On 6 September 2010 10:13, Ronald S. Bultje<rsbultje at gmail.com>
>>>>  wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> On Mon, Sep 6, 2010 at 5:54 AM, Vitor Sessak<vitor1001 at gmail.com>
>>>>>  wrote:
>>>>>>
>>>>>> On 09/06/2010 02:46 AM, Marcelo Galvão Póvoa wrote:
>>>>>>>
>>>>>>> Ok, fortunately I've found the bug!
>>>>>>>
>>>>>>> It was just a MIN_ISF_SPACING parameter which I extracted from the
>>>>>>> reference code but was unsure about it's Q level. After some time, I
>>>>>>> thought I have it figured out but I was wrong. Now I know the answer
>>>>>>> the hard way...
>>>>>>>
>>>>>>> The clipping and the sharp peaks are gone, the waveforms are really
>>>>>>> close now!
>>>>>>
>>>>>> That's great news!
>>>>>>
>>>>>>> Also, the stddev against the reference decoder decreased a
>>>>>>> lot (it was ~884 before):
>>>>>>> all_men.awb stddev:   51.72 PSNR: 62.05 MAXDIFF: 1089 bytes:
>>>>>>> 473600/
>>>>>>> 473600
>>>>>>
>>>>>> stddev of 51 looks pretty good to me for this case.
>>>>>
>>>>> Maxdiff of 1089 looks like a lot to me, with a low stddev that
>>>>> suggests that one particular part is off. Can you trace which part is
>>>>> off and why (phase shift vs. actual bug)?
>>>>>
>>>>
>>>> Sorry, but can you suggest a way of doing it?
>>>
>>> Your method of inverting one sample and summing in audacity would work on
>>> showing where it is happening (some point will have an amplitude of
>>> 1089).
>>> To know if is a phase shift or a bug, you will have to compare visually
>>> both
>>> waves.
>>>
>>
>> I don't know exactly how to detect a phase shift this way but the
>> difference waveform I obtained [1] has some peaks at the sibilant
>> parts I think. Probably just where the high band is louder.
>>
>>>> Also, what do MAXDIFF
>>>> and the "2" at the end of the command line mean?
>>>
>>> MAXDIFF is the biggest difference among two samples. The "2" at the end
>>> of
>>> the command line says to read two-byte integers (16-bit). If you were
>>> comparing video pixels, you would use "1". You can also see the source of
>>> tiny_psnr.c, it is pretty simple.
>>>
>>>> This sample have long silence parts and I'm comparing my floating
>>>> point implementation to the reference 16-bit fixed point. How close
>>>> you think they should be?
>>>
>>> A very small stddev (<  1.00) would assure there is no bug in your
>>> decoder,
>>> but the fact that it is large does not means there is one.
>>>
>>> I suggest you do the following test:
>>>
>>> a) Get a biggish file (>  30 minutes)
>>> b) Convert it to the a WAV with the sample rate and number of channel the
>>> AMR encoder takes as input
>>> c) Encode the file obtained in (b) it with the reference encoder
>>> d) Decode the file obtained in (c) with the reference decoder
>>> e) Decode the file obtained in (c) with ffamrwb
>>> f) Compare the stddev of files obtained in (b) and (d) with that of (b)
>>> and
>>> (e). If file decoded with ffamr are as close to the original as that
>>> decoded
>>> with the reference decoder, it's good.
>>>
>>
>> Results:
>> $ ./tests/tiny_psnr ~/ref_pod.wav ~/orig_pod.wav 2
>> stddev: 2599.69 PSNR: 28.03 MAXDIFF:39592 bytes: 76480640/ 76480660
>> $ ./tests/tiny_psnr ~/my_pod.wav ~/orig_pod.wav 2
>> stddev: 2600.02 PSNR: 28.03 MAXDIFF:39653 bytes: 76480640/ 76480660
>> $ ./tests/tiny_psnr ~/my_pod.wav ~/ref_pod.wav 2
>
>
> Hmm, the files have different sizes. Are you sure you are not comparing
> files shifted of a few bytes? One parameter of tiny_psnr is a shift between
> the two files. Does
>
> tiny_psnr ~/ref_pod.wav ~/orig_pod.wav 2 10
>
> Gives a much worse result? If the shift you are using now (zero) is correct,
> changing it to anything else should make stddev much bigger. Can you also
> put the wav files somewhere I can download? If you have a problem of quota,
> you can use our FTP server as explained in [1].
>

Now that seems weird:

$ ./tests/tiny_psnr ~/my_pod2.wav ~/orig_pod.wav 2 10
stddev: 2575.45 PSNR: 28.11 MAXDIFF:46172 bytes: 76480630/ 76480660

$ ./tests/tiny_psnr ~/my_pod2.wav ~/orig_pod.wav 2 -20
stddev: 2524.06 PSNR: 28.29 MAXDIFF:45328 bytes: 76480640/ 76480640

$ ./tests/tiny_psnr ~/my_pod2.wav ~/orig_pod.wav 2 200
stddev: 2090.99 PSNR: 29.92 MAXDIFF:46167 bytes: 76480440/ 76480660

I will upload the files later. Probably it will take some time.

-- 
Marcelo