[FFmpeg-cvslog] webp: Fix alpha decoding

[Mark Thompson]

ffmpeg | branch: master | Mark Thompson <sw at jkqxz.net> | Fri Feb 17 23:14:19 2017 +0000| [7cb9296db872c4221453e5411f242ebcfca62664] | committer: Mark Thompson

webp: Fix alpha decoding

This was broken by 4e528206bc4d968706401206cf54471739250ec7 - the webp
decoder was assuming that it could set the output pixfmt of the vp8
decoder directly, but after that change it no longer could because
ff_get_format() was used instead.  This adds an internal get_format()
callback to webp use of the vp8 decoder to override the pixfmt
appropriately.

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7cb9296db872c4221453e5411f242ebcfca62664
---

 libavcodec/webp.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/libavcodec/webp.c b/libavcodec/webp.c
index 4548e5fb3b..18d68e9140 100644
--- a/libavcodec/webp.c
+++ b/libavcodec/webp.c
@@ -1288,6 +1288,16 @@ static int vp8_lossy_decode_alpha(AVCodecContext *avctx, AVFrame *p,
     return 0;
 }
 
+static enum AVPixelFormat webp_get_format(AVCodecContext *avctx,
+                                          const enum AVPixelFormat *formats)
+{
+    WebPContext *s = avctx->priv_data;
+    if (s->has_alpha)
+        return AV_PIX_FMT_YUVA420P;
+    else
+        return AV_PIX_FMT_YUV420P;
+}
+
 static int vp8_lossy_decode_frame(AVCodecContext *avctx, AVFrame *p,
                                   int *got_frame, uint8_t *data_start,
                                   unsigned int data_size)
@@ -1299,8 +1309,7 @@ static int vp8_lossy_decode_frame(AVCodecContext *avctx, AVFrame *p,
     if (!s->initialized) {
         ff_vp8_decode_init(avctx);
         s->initialized = 1;
-        if (s->has_alpha)
-            avctx->pix_fmt = AV_PIX_FMT_YUVA420P;
+        avctx->get_format = webp_get_format;
     }
     s->lossless = 0;