[x265] [PATCH] Implementation of low-pass subband dct approximation

[Tom Vaughan]

Hi Humberto,
We need to understand the effect on performance and encoding efficiency
under different conditions (quality levels - or QPs, performance presets,
and picture sizes).  Once we have a better understanding, we can figure out
when to turn it on.  It's likely to be something that can help the fastest
presets go faster, where encoding efficiency is less of a priority than
performance.  But as you noted, it may also be something that we would only
enable when x265 is using higher QP values.

I've asked our team to do some experiments, but if you have any date from
your experiments we would love to see it.

Thanks,
Tom

-----Original Message-----
From: x265-devel [mailto:x265-devel-bounces at videolan.org] On Behalf Of
Mont3z Claros
Sent: Monday, November 6, 2017 7:28 AM
To: Development for x265
Subject: Re: [x265] [PATCH] Implementation of low-pass subband dct
approximation

Hi,

thanks for you comment and thanks for accepting my contribution.

I did so many tests using constant QP that I forgot about the other more
important rate-control modes. We could relax this by just ORing it with
limits for those other modes. However I understand that ideally the
application of this transformation is a function of QP and the blocks mean
deviation. I've tried to do this indirectly by fixing the QP's limit and by
using the transformation only on 16x16 and 32x32 blocks.

I'll try figure out a better way to best add those limitations.
Please, let me know if you can think of anything that might help.

Humberto

>> +
>>  void setupAliasPrimitives(EncoderPrimitives &p)  {  #if
>> HIGH_BIT_DEPTH @@ -256,6 +271,11 @@  #endif
>>
>>          setupAliasPrimitives(primitives);
>> +
>> +        if (param->bLowPassDct && param->rc.qp > 20)
>> +        {
>> +            enableLowpassDCTPrimitives(primitives);
>> +        }
>
>
> Essentially this means that you enable lowpass-dct only when doing
> constant QP encodes. You could consider relaxing this to enable the
> option for other rate-control modes as well (ABR/CRF) and have some
> directives in your docs as to when the feature is better to use.
> Hard-coding the limits in the code isn't a great idea, IMO.
>
>>
>>      }
>>
>>      x265_report_simd(param);
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/common/primitives.h
>> --- a/source/common/primitives.h        Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/common/primitives.h        Sat Oct 14 09:19:03 2017 -0700
>> @@ -259,8 +259,12 @@
>>       * primitives will leave 64x64 pointers NULL.  Indexed by LumaCU */
>>      struct CU
>>      {
>> -        dct_t           dct;
>> -        idct_t          idct;
>> +        dct_t           dct;    // active dct transformation
>> +        idct_t          idct;   // active idct transformation
>> +
>> +        dct_t           standard_dct;   // original dct function, used
>> by
>> lowpass_dct
>> +        dct_t           lowpass_dct;    // lowpass dct approximation
>> +
>>          calcresidual_t  calcresidual;
>>          pixel_sub_ps_t  sub_ps;
>>          pixel_add_ps_t  add_ps;
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/x265.h
>> --- a/source/x265.h     Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/x265.h     Sat Oct 14 09:19:03 2017 -0700
>> @@ -1505,6 +1505,11 @@
>>
>>      /* Disable lookahead */
>>      int       bDisableLookahead;
>> +
>> +    /* Use low-pass truncated dct approximation
>> +    *  This DCT approximation is less computational intensive and
>> + gives
>> results close to
>> +    *  standard DCT for QP >= 23 */
>> +    int       bLowPassDct;
>>  } x265_param;
>>
>>  /* x265_param_alloc:
>> diff -r 6a310b24c6a2 -r 893b36b82133 source/x265cli.h
>> --- a/source/x265cli.h  Thu Nov 02 12:17:29 2017 +0530
>> +++ b/source/x265cli.h  Sat Oct 14 09:19:03 2017 -0700
>> @@ -282,6 +282,7 @@
>>      { "force-flush",    required_argument, NULL, 0 },
>>      { "splitrd-skip",         no_argument, NULL, 0 },
>>      { "no-splitrd-skip",      no_argument, NULL, 0 },
>> +    { "lowpass-dct",          no_argument, NULL, 0 },
>>      { 0, 0, 0, 0 },
>>      { 0, 0, 0, 0 },
>>      { 0, 0, 0, 0 },
>> @@ -543,6 +544,7 @@
>>      H1("-r/--recon <filename>            Reconstructed raw image YUV or
>> Y4M output file name\n");
>>      H1("   --recon-depth <integer>       Bit-depth of reconstructed raw
>> image file. Defaults to input bit depth, or 8 if Y4M\n");
>>      H1("   --recon-y4m-exec <string>     pipe reconstructed frames to
>> Y4M
>> viewer, ex:\"ffplay -i pipe:0 -autoexit\"\n");
>> +    H0("   --lowpass-dct                 Use low-pass subband dct
>> approximation. Default %s\n", OPT(param->bLowPassDct));
>>      H1("\nExecutable return codes:\n");
>>      H1("    0 - encode successful\n");
>>      H1("    1 - unable to parse command line\n");
>>
>> _______________________________________________
>> x265-devel mailing list
>> x265-devel at videolan.org
>> https://mailman.videolan.org/listinfo/x265-devel
>>
>
>
> _______________________________________________
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> x265-devel at videolan.org
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>
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