From e7e243b2ee08313c0fb6a75c1c8c62c78af00d8b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20B=C5=93sch?= <ubitux@gmail.com>
Date: Thu, 18 Apr 2013 03:35:20 +0200
Subject: [PATCH] gif: use only one graphic control extension block per image.

---
 libavcodec/gif.c  | 29 ++++++-----------------------
 libavformat/gif.c | 28 ++++++++++++++++++++++++++--
 2 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/libavcodec/gif.c b/libavcodec/gif.c
index b35cfd1..0df302e 100644
--- a/libavcodec/gif.c
+++ b/libavcodec/gif.c
@@ -56,28 +56,6 @@ static int gif_image_write_image(AVCodecContext *avctx,
     int x_start = 0, y_start = 0;
     const uint8_t *ptr;
 
-    /* Mark one colour as transparent if the input palette contains at least
-     * one colour that is more than 50% transparent. */
-    if (palette) {
-        unsigned i, smallest_alpha = 0xFF, alpha_component = 0;
-        for (i = 0; i < AVPALETTE_COUNT; i++) {
-            const uint32_t v = palette[i];
-            if (v >> 24 < smallest_alpha) {
-                smallest_alpha = v >> 24;
-                alpha_component = i;
-            }
-        }
-        if (smallest_alpha < 128) {
-            bytestream_put_byte(bytestream, 0x21); /* Extension Introducer */
-            bytestream_put_byte(bytestream, 0xf9); /* Graphic Control Label */
-            bytestream_put_byte(bytestream, 0x04); /* block length */
-            bytestream_put_byte(bytestream, 0x01); /* Transparent Color Flag */
-            bytestream_put_le16(bytestream, 0x00); /* no delay */
-            bytestream_put_byte(bytestream, alpha_component);
-            bytestream_put_byte(bytestream, 0x00);
-        }
-    }
-
     /* Crop image */
     // TODO support with palette change
     if (s->last_frame && !palette) {
@@ -210,8 +188,13 @@ static int gif_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     p->pict_type = AV_PICTURE_TYPE_I;
     p->key_frame = 1;
 
-    if (avctx->pix_fmt == AV_PIX_FMT_PAL8)
+    if (avctx->pix_fmt == AV_PIX_FMT_PAL8) {
+        uint8_t *pal_exdata = av_packet_new_side_data(pkt, AV_PKT_DATA_PALETTE, AVPALETTE_SIZE);
+        if (!pal_exdata)
+            return AVERROR(ENOMEM);
+        memcpy(pal_exdata, p->data[1], AVPALETTE_SIZE);
         palette = (uint32_t*)p->data[1];
+    }
 
     gif_image_write_image(avctx, &outbuf_ptr, end, palette, pict->data[0], pict->linesize[0]);
     if (!s->last_frame) {
diff --git a/libavformat/gif.c b/libavformat/gif.c
index 3d86f23..f26d537 100644
--- a/libavformat/gif.c
+++ b/libavformat/gif.c
@@ -102,15 +102,39 @@ static int gif_write_header(AVFormatContext *s)
 
 static int gif_write_packet(AVFormatContext *s, AVPacket *pkt)
 {
+    int size;
     AVCodecContext *enc = s->streams[pkt->stream_index]->codec;
     AVIOContext *pb = s->pb;
     int jiffies;
+    uint8_t flags = 0x4, transparent_color_index = 0x1f;
+    const uint32_t *palette;
+
+    /* Mark one colour as transparent if the input palette contains at least
+     * one colour that is more than 50% transparent. */
+    palette = (uint32_t*)av_packet_get_side_data(pkt, AV_PKT_DATA_PALETTE, &size);
+    if (palette && size != AVPALETTE_SIZE) {
+        av_log(s, AV_LOG_ERROR, "Invalid palette extradata\n");
+        return AVERROR_INVALIDDATA;
+    }
+    if (palette) {
+        unsigned i, smallest_alpha = 0xff;
+
+        for (i = 0; i < AVPALETTE_COUNT; i++) {
+            const uint32_t v = palette[i];
+            if (v >> 24 < smallest_alpha) {
+                smallest_alpha = v >> 24;
+                transparent_color_index = i;
+            }
+        }
+        if (smallest_alpha < 128)
+            flags |= 0x1; /* Transparent Color Flag */
+    }
 
     /* graphic control extension block */
     avio_w8(pb, 0x21);
     avio_w8(pb, 0xf9);
     avio_w8(pb, 0x04); /* block size */
-    avio_w8(pb, 0x04); /* flags */
+    avio_w8(pb, flags);
 
     /* 1 jiffy is 1/70 s */
     /* the delay_time field indicates the number of jiffies - 1 */
@@ -121,7 +145,7 @@ static int gif_write_packet(AVFormatContext *s, AVPacket *pkt)
 
     avio_wl16(pb, jiffies);
 
-    avio_w8(pb, 0x1f); /* transparent color index */
+    avio_w8(pb, transparent_color_index);
     avio_w8(pb, 0x00);
 
     avio_write(pb, pkt->data, pkt->size);
-- 
1.8.2.1