[FFmpeg-trac] #7774(avcodec:new): ProRes Scanned Alpha omitting last run of a slice if it's length 0

[FFmpeg]

#7774: ProRes Scanned Alpha omitting last run of a slice if it's length 0
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             Reporter:  vinlai   |                     Type:  defect
               Status:  new      |                 Priority:  normal
            Component:  avcodec  |                  Version:  unspecified
             Keywords:           |               Blocked By:
             Blocking:           |  Reproduced by developer:  0
Analyzed by developer:  0        |
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 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.

 ----

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

 Thanks.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7774>
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