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avcodec/gifenc: Add global_palette option 

This option will disable the writing of the global palette in global
GIF header if it is set to 0, causing only the frame-level palette
to ever be written.

This will be useful later on when further frame-level palette
optimizations are introduced.

The default is 1, which maintains current default behavior.

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
This commit is contained in:
Derek Buitenhuis 2021-02-20 17:22:51 +00:00
parent 6eab25fd13
commit 5f2804aba7
1 changed files with 13 additions and 8 deletions
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21
libavcodec/gif.c
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@ -51,6 +51,7 @@ typedef struct GIFContext {
AVFrame *last_frame;
int flags;
int image;
int use_global_palette;
uint32_t palette[AVPALETTE_COUNT]; ///< local reference palette for !pal8
int palette_loaded;
int transparent_index;
@ -293,12 +294,14 @@ static int gif_image_write_image(AVCodecContext *avctx,
bcid = get_palette_transparency_index(global_palette);
bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
bytestream_put_byte(bytestream, ((uint8_t) s->use_global_palette << 7) | 0x70 | (s->use_global_palette ? 7 : 0)); /* flags: global clut, 256 entries */
bytestream_put_byte(bytestream, bcid < 0 ? DEFAULT_TRANSPARENCY_INDEX : bcid); /* background color index */
bytestream_put_byte(bytestream, aspect);
for (int i = 0; i < 256; i++) {
const uint32_t v = global_palette[i] & 0xffffff;
bytestream_put_be24(bytestream, v);
if (s->use_global_palette) {
for (int i = 0; i < 256; i++) {
const uint32_t v = global_palette[i] & 0xffffff;
bytestream_put_be24(bytestream, v);
}
}
}
@ -330,15 +333,16 @@ static int gif_image_write_image(AVCodecContext *avctx,
bytestream_put_le16(bytestream, width);
bytestream_put_le16(bytestream, height);
if (!palette) {
bytestream_put_byte(bytestream, 0x00); /* flags */
} else {
if (palette || !s->use_global_palette) {
const uint32_t *pal = palette ? palette : s->palette;
unsigned i;
bytestream_put_byte(bytestream, 1<<7 | 0x7); /* flags */
for (i = 0; i < AVPALETTE_COUNT; i++) {
const uint32_t v = palette[i];
const uint32_t v = pal[i];
bytestream_put_be24(bytestream, v);
}
} else {
bytestream_put_byte(bytestream, 0x00); /* flags */
}
bytestream_put_byte(bytestream, 0x08);
@ -473,6 +477,7 @@ static const AVOption gif_options[] = {
{ "offsetting", "enable picture offsetting", 0, AV_OPT_TYPE_CONST, {.i64=GF_OFFSETTING}, INT_MIN, INT_MAX, FLAGS, "flags" },
{ "transdiff", "enable transparency detection between frames", 0, AV_OPT_TYPE_CONST, {.i64=GF_TRANSDIFF}, INT_MIN, INT_MAX, FLAGS, "flags" },
{ "gifimage", "enable encoding only images per frame", OFFSET(image), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS },
{ "global_palette", "write a palette to the global gif header where feasible", OFFSET(use_global_palette), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS },
{ NULL }
};