I would prefer with memory log removed....
Probably fine anyway.
On Sat, Feb 20, 2021 at 8:24 PM Derek Buitenhuis <derek.buitenh...@gmail.com>
wrote:
> GIF palette entries are not compressed, and writing 256 entries,
> which can be up to every frame, uses a significant amount of
> space, especially in extreme cases, where palettes can be very
> small.
>
> Example, first six seconds of Tears of Steel, palette generated
> with libimagequant, 320x240 resolution, and with transparency
> optimization + per frame palette:
>
> * Before patch: 186765 bytes
> * After patch: 77895 bytes
>
> Signed-off-by: Derek Buitenhuis <derek.buitenh...@gmail.com>
> ---
> Changes since v2:
> * shrunk_buf allocated only once per encoder instance.
> * Does not use temporary pointers during remapping.
> ---
> libavcodec/gif.c | 68 +++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 65 insertions(+), 3 deletions(-)
>
> diff --git a/libavcodec/gif.c b/libavcodec/gif.c
> index 8c07ee2769..ff0d50cb44 100644
> --- a/libavcodec/gif.c
> +++ b/libavcodec/gif.c
> @@ -47,6 +47,7 @@ typedef struct GIFContext {
> const AVClass *class;
> LZWState *lzw;
> uint8_t *buf;
> + uint8_t *shrunk_buf;
> int buf_size;
> AVFrame *last_frame;
> int flags;
> @@ -63,6 +64,38 @@ enum {
> GF_TRANSDIFF = 1<<1,
> };
>
> +static void shrink_palette(const uint32_t *src, uint8_t *map,
> + uint32_t *dst, size_t *palette_count)
> +{
> + size_t colors_seen = 0;
> +
> + for (size_t i = 0; i < AVPALETTE_COUNT; i++) {
> + int seen = 0;
> + for (size_t c = 0; c < colors_seen; c++) {
> + if (src[i] == dst[c]) {
> + seen = 1;
> + break;
> + }
> + }
> + if (!seen) {
> + dst[colors_seen] = src[i];
> + map[i] = colors_seen;
> + colors_seen++;
> + }
> + }
> +
> + *palette_count = colors_seen;
> +}
> +
> +static void remap_frame_to_palette(const uint8_t *src, int src_linesize,
> + uint8_t *dst, int dst_linesize,
> + int w, int h, uint8_t *map)
> +{
> + for (int i = 0; i < h; i++)
> + for (int j = 0; j < w; j++)
> + dst[i * dst_linesize + j] = map[src[i * src_linesize + j]];
> +}
> +
> static int is_image_translucent(AVCodecContext *avctx,
> const uint8_t *buf, const int linesize)
> {
> @@ -267,6 +300,17 @@ static int gif_image_write_image(AVCodecContext
> *avctx,
> int x_start = 0, y_start = 0, trans = s->transparent_index;
> int bcid = -1, honor_transparency = (s->flags & GF_TRANSDIFF) &&
> s->last_frame && !palette;
> const uint8_t *ptr;
> + uint32_t shrunk_palette[AVPALETTE_COUNT];
> + uint8_t map[AVPALETTE_COUNT] = { 0 };
> + size_t shrunk_palette_count = 0;
> +
> + /*
> + * We memset to 0xff instead of 0x00 so that the transparency
> detection
> + * doesn't pick anything after the palette entries as the transparency
> + * index, and because GIF89a requires us to always write a power-of-2
> + * number of palette entries.
> + */
> + memset(shrunk_palette, 0xff, AVPALETTE_SIZE);
>
> if (!s->image && is_image_translucent(avctx, buf, linesize)) {
> gif_crop_translucent(avctx, buf, linesize, &width, &height,
> &x_start, &y_start);
> @@ -335,9 +379,14 @@ static int gif_image_write_image(AVCodecContext
> *avctx,
>
> if (palette || !s->use_global_palette) {
> const uint32_t *pal = palette ? palette : s->palette;
> + unsigned pow2_count;
> unsigned i;
> - bytestream_put_byte(bytestream, 1<<7 | 0x7); /* flags */
> - for (i = 0; i < AVPALETTE_COUNT; i++) {
> +
> + shrink_palette(pal, map, shrunk_palette, &shrunk_palette_count);
> + pow2_count = av_log2(shrunk_palette_count - 1);
> +
> + bytestream_put_byte(bytestream, 1<<7 | pow2_count); /* flags */
> + for (i = 0; i < 1 << (pow2_count + 1); i++) {
> const uint32_t v = pal[i];
> bytestream_put_be24(bytestream, v);
> }
> @@ -350,7 +399,19 @@ static int gif_image_write_image(AVCodecContext
> *avctx,
> ff_lzw_encode_init(s->lzw, s->buf, s->buf_size,
> 12, FF_LZW_GIF, 1);
>
> - ptr = buf + y_start*linesize + x_start;
> + if (shrunk_palette_count) {
> + if (!s->shrunk_buf) {
> + s->shrunk_buf = av_malloc(avctx->height * linesize);
> + if (!s->shrunk_buf) {
> + av_log(avctx, AV_LOG_ERROR, "Could not allocated remapped
> frame buffer.\n");
> + return AVERROR(ENOMEM);
> + }
> + }
> + remap_frame_to_palette(buf, linesize, s->shrunk_buf, linesize,
> avctx->width, avctx->height, map);
> + ptr = s->shrunk_buf + y_start*linesize + x_start;
> + } else {
> + ptr = buf + y_start*linesize + x_start;
> + }
> if (honor_transparency) {
> const int ref_linesize = s->last_frame->linesize[0];
> const uint8_t *ref = s->last_frame->data[0] +
> y_start*ref_linesize + x_start;
> @@ -464,6 +525,7 @@ static int gif_encode_close(AVCodecContext *avctx)
>
> av_freep(&s->lzw);
> av_freep(&s->buf);
> + av_freep(&s->shrunk_buf);
> s->buf_size = 0;
> av_frame_free(&s->last_frame);
> av_freep(&s->tmpl);
> --
> 2.30.0
>
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