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webp-container-spec.txt: clarify some SHOULDs

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for compatibility SHOULDs are left as is with some additional
description given of behavior if the recommendation is ignored.

Change-Id: I7a25b1a6fd9f9594390c30fce3af5ca17c3158c0
This commit is contained in:
James Zern 2022-08-01 19:06:01 -07:00
parent bec2c88a11
commit 1a64a7e649
1 changed files with 9 additions and 6 deletions
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15
doc/webp-container-spec.txt
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@ -129,7 +129,8 @@ Chunk Size: 32 bits (_uint32_)
Chunk Payload: _Chunk Size_ bytes Chunk Payload: _Chunk Size_ bytes
: The data payload. If _Chunk Size_ is odd, a single padding byte -- that : The data payload. If _Chunk Size_ is odd, a single padding byte -- that
SHOULD be `0` -- is added. SHOULD be `0` to conform with RIFF -- is added. Applications MAY use
another value, but readers may fail to parse the file.
**Note:** RIFF has a convention that all-uppercase chunk FourCCs are standard **Note:** RIFF has a convention that all-uppercase chunk FourCCs are standard
chunks that apply to any RIFF file format, while FourCCs specific to a file chunks that apply to any RIFF file format, while FourCCs specific to a file
@ -165,9 +166,10 @@ File Size: 32 bits (_uint32_)
A WebP file MUST begin with a RIFF header with the FourCC 'WEBP'. The file size A WebP file MUST begin with a RIFF header with the FourCC 'WEBP'. The file size
in the header is the total size of the chunks that follow plus `4` bytes for in the header is the total size of the chunks that follow plus `4` bytes for
the 'WEBP' FourCC. The file SHOULD NOT contain anything after it. As the size the 'WEBP' FourCC. The file SHOULD NOT contain anything after it. Readers MAY
of any chunk is even, the size given by the RIFF header is also even. The parse such files, ignoring the trailing data. As the size of any chunk is even,
contents of individual chunks will be described in the following sections. the size given by the RIFF header is also even. The contents of individual
chunks will be described in the following sections.
Simple File Format (Lossy) Simple File Format (Lossy)
@ -210,8 +212,9 @@ The VP8 bitstream format specification can be found at [VP8 Data Format and
Decoding Guide][vp8spec]. Note that the VP8 frame header contains the VP8 frame Decoding Guide][vp8spec]. Note that the VP8 frame header contains the VP8 frame
width and height. That is assumed to be the width and height of the canvas. width and height. That is assumed to be the width and height of the canvas.
The VP8 specification describes how to decode the image into Y'CbCr The VP8 specification describes how to decode the image into Y'CbCr format. To
format. To convert to RGB, Rec. 601 SHOULD be used. convert to RGB, Rec. 601 SHOULD be used. Applications MAY use another
conversion method, but visual results may differ among decoders.
Simple File Format (Lossless) Simple File Format (Lossless)