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Fix "all|no frames are keyframes" settings.

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Documentation says: "if kmin == 0, then key-frame insertion is disabled;
and if kmax == 0, then all frames will be key-frames."
Reading this, you'd expect that if kmax == 0, then with any kmin <= 0
all frames will be key-frames. But actually the kmin <= 0 test is caught
first and you get the opposite (no keyframes but the first). You'd have
instead to set kmax == 0 and any value kmin > 0, which is absolutely
counter-intuitive (reversing order).
Moreover kmax == 1 has no valid kmin (kmin == 1 conflicts with the
`kmax > kmin` rule and kmin == 0 conflicts with `kmin >= kmax / 2 + 1`).
So it should be considered an exception too.

Instead I propose this new logic:
- kmax == 1 means that all frames are keyframes (you are explicitly
  requesting a keyframe every 1 frame at most, i.e. all frames).
- kmax == 0 means no keyframes (you ask for a keyframe every 0 frames,
  i.e. never).
This is more "logical" language-wise, and also does not involve any
conflicts about what if both kmax and kmin are 0, since now a single
property value is meaningful for the 2 exceptional cases.

Change-Id: Ia90fb963bc26904ff078d2e4ef9f74b22b13a0fd
(cherry picked from commit 2dc0bdcaee)
This commit is contained in:
Jehan 2016-11-26 01:25:49 +01:00 committed by James Zern
parent f4dc56fd77
commit 32ed856f60
3 changed files with 13 additions and 12 deletions
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7
man/gif2webp.1
View File

@ -1,5 +1,5 @@
.\" Hey, EMACS: -*- nroff -*-
.TH GIF2WEBP 1 "June 23, 2016"
.TH GIF2WEBP 1 "January 25, 2017"
.SH NAME
gif2webp \- Convert a GIF image to WebP
.SH SYNOPSIS
@ -68,8 +68,9 @@ Specify the minimum and maximum distance between consecutive key frames
some key frames into the output animation as needed so that this criteria is
satisfied.
.br
A 'kmin' value of 0 will turn off insertion of key frames. A 'kmax' value of 0
will result in all frames being key frames.
A 'kmax' value of 0 will turn off insertion of key frames. A 'kmax' value of 1
will result in all frames being key frames. 'kmin' value is not taken into
account in both these special cases.
Typical values are in the range 3 to 30. Default values are kmin = 9,
kmax = 17 for lossless compression and kmin = 3, kmax = 5 for lossy compression.
.br

9
src/mux/anim_encode.c
View File

@ -129,14 +129,13 @@ static void SanitizeEncoderOptions(WebPAnimEncoderOptions* const enc_options) {
DisableKeyframes(enc_options);
}
if (enc_options->kmin <= 0) {
DisableKeyframes(enc_options);
print_warning = 0;
}
if (enc_options->kmax <= 0) { // All frames will be key-frames.
if (enc_options->kmax == 1) { // All frames will be key-frames.
enc_options->kmin = 0;
enc_options->kmax = 0;
return;
} else if (enc_options->kmax <= 0) {
DisableKeyframes(enc_options);
print_warning = 0;
}
if (enc_options->kmin >= enc_options->kmax) {

9
src/webp/mux.h
View File

@ -21,7 +21,7 @@
extern "C" {
#endif
#define WEBP_MUX_ABI_VERSION 0x0107 // MAJOR(8b) + MINOR(8b)
#define WEBP_MUX_ABI_VERSION 0x0108 // MAJOR(8b) + MINOR(8b)
//------------------------------------------------------------------------------
// Mux API
@ -430,9 +430,10 @@ struct WebPAnimEncoderOptions {
// frames in the output. The library may insert some key
// frames as needed to satisfy this criteria.
// Note that these conditions should hold: kmax > kmin
// and kmin >= kmax / 2 + 1. Also, if kmin == 0, then
// key-frame insertion is disabled; and if kmax == 0,
// then all frames will be key-frames.
// and kmin >= kmax / 2 + 1. Also, if kmax <= 0, then
// key-frame insertion is disabled; and if kmax == 1,
// then all frames will be key-frames (kmin value does
// not matter for these special cases).
int allow_mixed; // If true, use mixed compression mode; may choose
// either lossy and lossless for each frame.
int verbose; // If true, print info and warning messages to stderr.