[FFmpeg-devel] [PATCH] Limit Rice parameter for progressive decoding in ALS

[Thilo Borgmann]

Am 13.02.10 20:54, schrieb Justin Ruggles:
> Thilo Borgmann wrote:
> 
>> Hi,
>>
>> as in $subject, the reference encoder limits the Rice parameter during
>> progressively coding the first few samples of a random access block.
>>
>> Yet another "feature" not specified in 14496-3...
> 
> Fun. Nice catch.
> 
> 
>> Regards,
>> Thilo
>>
>>
> 
>> Index: libavcodec/alsdec.c
>> ===================================================================
>> --- libavcodec/alsdec.c	(Revision 21799)
>> +++ libavcodec/alsdec.c	(Arbeitskopie)
>> @@ -192,6 +192,7 @@
>>      unsigned int frame_id;          ///< the frame ID / number of the current frame
>>      unsigned int js_switch;         ///< if true, joint-stereo decoding is enforced
>>      unsigned int num_blocks;        ///< number of blocks used in the current frame
>> +    unsigned int s_max;             ///< maximum Rice parameter allowed in entropy coding
>>      uint8_t *bgmc_lut;              ///< pointer at lookup tables used for BGMC
>>      unsigned int *bgmc_lut_status;  ///< pointer at lookup table status flags used for BGMC
>>      int ltp_lag_length;             ///< number of bits used for ltp lag value
>> @@ -720,9 +721,9 @@
>>          if (opt_order)
>>              bd->raw_samples[0] = decode_rice(gb, avctx->bits_per_raw_sample - 4);
>>          if (opt_order > 1)
>> -            bd->raw_samples[1] = decode_rice(gb, s[0] + 3);
>> +            bd->raw_samples[1] = decode_rice(gb, FFMIN(s[0] + 3, ctx->s_max));
>>          if (opt_order > 2)
>> -            bd->raw_samples[2] = decode_rice(gb, s[0] + 1);
>> +            bd->raw_samples[2] = decode_rice(gb, FFMIN(s[0] + 1, ctx->s_max));
>>  
>>          start = FFMIN(opt_order, 3);
>>      }
>> @@ -1508,6 +1509,11 @@
>>          avctx->bits_per_raw_sample = (sconf->resolution + 1) * 8;
>>      }
>>  
>> +    // set maximum Rice parameter for progressive decoding based on resolution
>> +    // This is not specified in 14496-3 but actually done by the reference
>> +    // codec RM22 revision 2.
>> +    ctx->s_max = (16 << (sconf->resolution > 1)) - 1;
>> +
> 
> It seems simpler to me to just do:
> ctx->s_max = sconf->resolution > 1 ? 31 : 15;

Well someone injected a little prudence about ?: into me... but ok,
revision 1 attached.

-Thilo
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