ProRes Scanned Alpha omitting last run of a slice if it's length 0

[vinlai]

Alpha encoded using prores_ks produces slices that omits the final run of a slice if it is length 0. This is the correct behaviour for non-alpha channels, however, the termination conditions are different for alpha.

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RDD36-2015:

7.1.1.4 AC Coefficients

They are terminated either by a non-zero array element—a level—or by reaching the end of the array.

7.1.2 Scanned Alpha

They terminate when one of the following occurs: two consecutive array elements have different values; the end of the array is reached; or the maximum permissible run length, 2048, is achieved.

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In summary, encoded Alpha should not be omitting the final run of a slice even if it is length 0.

Thanks.