Derek Buitenhuis: > 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> > --- > The global palette, if used, is no longer ever shrunk in v2 of this > patch. This is because just because any given frame doesn't reference > an index, doesn't mean a future frame won't. > --- > libavcodec/gif.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 69 insertions(+), 3 deletions(-) > > diff --git a/libavcodec/gif.c b/libavcodec/gif.c > index 8c07ee2769..420a1f523e 100644 > --- a/libavcodec/gif.c > +++ b/libavcodec/gif.c > @@ -63,6 +63,44 @@ 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) > +{ > + uint8_t *sptr = (uint8_t *) src;
Casting const away here is completely unnecessary as sptr is not used to modify what it points to; and actually sptr and dptr are completely unnecessary, too. > + uint8_t *dptr = dst; > + > + for (int i = 0; i < h; i++) { > + for (int j = 0; j < w; j++) > + dptr[j] = map[sptr[j]]; > + dptr += dst_linesize; > + sptr += src_linesize; > + } > +} > + > static int is_image_translucent(AVCodecContext *avctx, > const uint8_t *buf, const int linesize) > { > @@ -267,6 +305,18 @@ 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; > + uint8_t *shrunk_buf = NULL; > + > + /* > + * 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 +385,14 @@ 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 +405,17 @@ 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) { > + shrunk_buf = av_malloc(avctx->height * linesize); > + if (!shrunk_buf) { > + av_log(avctx, AV_LOG_ERROR, "Could not allocated remapped frame > buffer.\n"); > + return AVERROR(ENOMEM); > + } > + remap_frame_to_palette(buf, linesize, shrunk_buf, linesize, > avctx->width, avctx->height, map); > + ptr = 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; > @@ -383,6 +448,7 @@ static int gif_image_write_image(AVCodecContext *avctx, > len -= size; > } > bytestream_put_byte(bytestream, 0x00); /* end of image block */ > + av_freep(&shrunk_buf); > return 0; > } > > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".