[Ffmpeg-devel] FLAC encoder
Sun May 28 16:54:06 CEST 2006
Michael Niedermayer wrote:
> On Sun, May 28, 2006 at 12:32:36AM -0400, Justin Ruggles wrote:
>>Here is an updated version of the encoder.
>>What I did:
>>Instead of doing brute-force bit counts and gradient search for the
>>optimal rice parameters, I used the log2(mean_residual_value). This is
>>not 100% optimal for compression, but it's close, and it is much faster.
>> First, the mean is calculated for each partition on the highest order
>>level. Then, each lower level mean is calculated by averaging each pair
>>of partitions from the level above. In addition to calculating k, the
>>means are also used to estimate bit count.
> the same summing (of the most significant bits instead of all) from the
> previous 2 higher order partitions can be done with the exact method too
> (it was the simple but slower alternative i suggested)
I think I see what you're suggesting now. I could more quickly
calculate the sums for each k by doing partial sums for each of the 32
bit positions then getting the bit count for each k by summing all
partial sums for position k and above. Since my updated version
estimates k, this wouldn't really help, but when I add the brute-force
method back in, it will speed things up. I am understanding this right?
>> 8 0m13.858s 2189192 0.414 584
>>As a comparison, here is the same sample with the previous version:
>> 10 0m18.091s 2187875 0.413 583
>>It might be worth taking out one of the lower levels and adding the old
>>brute-force search back in as level 8.
> yes, iam in favor of this
Great. I'll put it back in and take out level 1, which seems to be
consistantly worse than level 0.
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