Cleanse GIF muxer and encoder.

This commit removes the badly duplicated code between the encoder and
the muxer. That may sound surprising, but the encoder is now responsible
from the encoding of the picture when muxing to a .gif file. It also
does not require anymore a manual user intervention such as a -pix_fmt
rgb24 to work properly. To summarize, output gif are now easier to
generate, code is saner and simpler, and files are smaller (thanks to
the lzw encoding which was unused so far with the default .gif output).
We can certainly make things even better, but this is the first step.

FATE is updated because of the output being produced by the encoder and
not the muxer (no lzw in the muxer), and in the seek test only the size
mismatches.

Fixes Ticket #2262

1 files changed, 40 insertions, 44 deletions

diff --git a/libavcodec/gif.c b/libavcodec/gif.c
index 98ab767c40..cd7b76155f 100644
--- a/libavcodec/gif.c
+++ b/libavcodec/gif.c
@@ -51,61 +51,54 @@ typedef struct {
     uint8_t *buf;
 } GIFContext;
 
-/* GIF header */
-static int gif_image_write_header(AVCodecContext *avctx,
-                                  uint8_t **bytestream, uint32_t *palette)
-{
-    int i;
-    unsigned int v, smallest_alpha = 0xFF, alpha_component = 0;
-
-    bytestream_put_buffer(bytestream, "GIF", 3);
-    bytestream_put_buffer(bytestream, "89a", 3);
-    bytestream_put_le16(bytestream, avctx->width);
-    bytestream_put_le16(bytestream, avctx->height);
-
-    bytestream_put_byte(bytestream, 0xf7); /* flags: global clut, 256 entries */
-    bytestream_put_byte(bytestream, 0x1f); /* background color index */
-    bytestream_put_byte(bytestream, 0); /* aspect ratio */
-
-    /* the global palette */
-    for(i=0;i<256;i++) {
-        v = palette[i];
-        bytestream_put_be24(bytestream, v);
-        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);
-    }
-
-    return 0;
-}
-
 static int gif_image_write_image(AVCodecContext *avctx,
                                  uint8_t **bytestream, uint8_t *end,
+                                 const uint32_t *palette,
                                  const uint8_t *buf, int linesize)
 {
     GIFContext *s = avctx->priv_data;
     int len = 0, height;
     const uint8_t *ptr;
-    /* image block */
 
+    /* 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);
+        }
+    }
+
+    /* image block */
     bytestream_put_byte(bytestream, 0x2c);
     bytestream_put_le16(bytestream, 0);
     bytestream_put_le16(bytestream, 0);
     bytestream_put_le16(bytestream, avctx->width);
     bytestream_put_le16(bytestream, avctx->height);
+
+    if (!palette) {
     bytestream_put_byte(bytestream, 0x00); /* flags */
-    /* no local clut */
+    } else {
+        unsigned i;
+        bytestream_put_byte(bytestream, 1<<7 | 0x7); /* flags */
+        for (i = 0; i < AVPALETTE_COUNT; i++) {
+            const uint32_t v = palette[i];
+            bytestream_put_be24(bytestream, v);
+        }
+    }
 
     bytestream_put_byte(bytestream, 0x08);
 
@@ -130,7 +123,6 @@ static int gif_image_write_image(AVCodecContext *avctx,
         len -= size;
     }
     bytestream_put_byte(bytestream, 0x00); /* end of image block */
-    bytestream_put_byte(bytestream, 0x3b);
     return 0;
 }
 
@@ -160,6 +152,7 @@ static int gif_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     GIFContext *s = avctx->priv_data;
     AVFrame *const p = &s->picture;
     uint8_t *outbuf_ptr, *end;
+    const uint32_t *palette = NULL;
     int ret;
 
     if ((ret = ff_alloc_packet2(avctx, pkt, avctx->width*avctx->height*7/5 + FF_MIN_BUFFER_SIZE)) < 0)
@@ -170,8 +163,11 @@ static int gif_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
     *p = *pict;
     p->pict_type = AV_PICTURE_TYPE_I;
     p->key_frame = 1;
-    gif_image_write_header(avctx, &outbuf_ptr, (uint32_t *)pict->data[1]);
-    gif_image_write_image(avctx, &outbuf_ptr, end, pict->data[0], pict->linesize[0]);
+
+    if (avctx->pix_fmt == AV_PIX_FMT_PAL8)
+        palette = (uint32_t*)p->data[1];
+
+    gif_image_write_image(avctx, &outbuf_ptr, end, palette, pict->data[0], pict->linesize[0]);
 
     pkt->size   = outbuf_ptr - pkt->data;
     pkt->flags |= AV_PKT_FLAG_KEY;