Ballot roman, security part, alt #250
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JeromeMartinez
suggested changes
Oct 19, 2020
| @@ -276,7 +276,7 @@ top16s = t >= 32768 ? ( t - 65536 ) : t | |||
| diag16s = tl >= 32768 ? ( tl - 65536 ) : tl | |||
| ``` | |||
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| Background: a two's complement 16-bit signed integer was used for storing Sample values in all known implementations of FFV1 bitstream. So in some circumstances, the most significant bit was wrongly interpreted (used as a sign bit instead of the 16th bit of an unsigned integer). Note that when the issue was discovered, the only configuration of all known implementations being impacted is 16-bit YCbCr with no Pixel transformation with Range Coder coder, as other potentially impacted configurations (e.g. 15/16-bit JPEG2000-RCT with Range Coder coder, or 16-bit content with Golomb Rice coder) were implemented nowhere [@!ISO.15444-1.2016]. In the meanwhile, 16-bit JPEG2000-RCT with Range Coder coder was implemented without this issue in one implementation and validated by one conformance checker. It is expected (to be confirmed) to remove this exception for the median predictor in the next version of the FFV1 bitstream. | |||
| Background: a two's complement 16-bit signed integer was used for storing Sample values in all known implementations of FFV1 bitstream (see (#ffv1-implementations)). So in some circumstances, the most significant bit was wrongly interpreted (used as a sign bit instead of the 16th bit of an unsigned integer). Note that when the issue was discovered, the only configuration of all known implementations being impacted is 16-bit YCbCr with no Pixel transformation with Range Coder coder, as other potentially impacted configurations (e.g. 15/16-bit JPEG2000-RCT with Range Coder coder, or 16-bit content with Golomb Rice coder) were implemented nowhere [@!ISO.15444-1.2016]. In the meanwhile, 16-bit JPEG2000-RCT with Range Coder coder was implemented without this issue in one implementation and validated by one conformance checker. It is expected (to be confirmed) to remove this exception for the median predictor in the next version of the FFV1 bitstream. | |||
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the "all known implementations of FFV1 bitstream" wording is 3x in the spec, so this change should be 3x.
rfc_backmatter.md
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| <front> | ||
| <title>FFV1 Decoder in Go</title> | ||
| <author initials="D." surname="Buitenhuis" fullname="Derek Buitenhuis"/> | ||
| <date year="undated" /> |
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I added a piece about the FFV1 implementation within MediaConch to the draft appendix on notable FFV1 implementations. CC'ing @mcr on this though in regards to any particular conflicts of interest here as both myself and @JeromeMartinez managed the referenced MediaConch project. |
JeromeMartinez
approved these changes
Oct 19, 2020
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Pointing to reference implementations as a non-normative reference shouldn't be a problem. |
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this is an alternate to #249