[FFmpeg-devel] GSoC VQA v3 : some more help needed

[Steven Zakulec]

On Sat, Apr 4, 2009 at 6:43 PM, Vitor Sessak <vitor1001 at gmail.com> wrote:

> The Deep Explorer wrote:
>
>> Hi all,
>>    I need some help in understanding how each frame is decoded in
>>  VQA v3. Please let me know how to proceed on the following :
>>
>>
>> 1) VPTR Decoding
>>
>> Steps :
>>
>> Read 1 short int ( 2 bytes)
>>
>
> From the doc:
>
>  Here's a list of the prefixes I encountered and their description (Val is
>> the short int value):
>>
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> So this short int you read is called "Val" in the doc
>
>  Read bits 15,14,13 and based on the command do actions.
>>
>> The document says e.g. :
>>
>>
>>     a) 000 - Skip Count blocks. Count is (Val & 0x1fff).
>>
>>        What is the Count blocks ?
>>
>
> I think you got confused by a var names. Read it this way:
>
> 000 - Skip "n" blocks, where n = (Val & 0x1fff)
>
>      b) 001 - Write block number (Val & 0xff) Count times.
>>              Count is (((Val/256) & 0x1f)+1)*2. Note that this can
>>              only index the first 256 blocks.
>>
>>              What is the block number ?
>>
>
> 001 - Write block number "idx" "k" times. idx = (Val & 0xff) and k =
> (((Val/256) & 0x1f)+1)*2.
>
>  <<Every row of blocks is processed individually of others.
>> When you encounter the end of a row, proceed to the next row
>> (blocks are processed left to right, top to down).
>> Repeat this process until all blocks in the frame are covered and
>> that's it!>>
>>
>> So is this the layout mechanism for v3 ? How are Count, Block, and Val
>> are related.
>>
>> There are two for loops, first one for the  y axis and the second one for
>> the x axis for the v1 and v2. so in case3 will the decoding of vptr will
>> take
>> place ? Read the three bits and then do the actions as specified ?
>>
>>
>>
>> 2) For VPRZ, first decode it with format80 and then follow the vptR thing
>>   so the VPRZ is dependent on the VPTR :)
>>
>
> Yes, so I suggest you try to find a sample with VPTR frames so you can test
> it before trying to decode VPRZ.
>
> -Vitor
>
> Some brief research indicates that
http://samples.mplayerhq.hu/game-formats/vqa/bladerunner/ contains multiple
samples with VPTR.