ffmpeg: select best pixel format for the encoder if no exact match.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

ffmpeg.c

@@ -764,6 +764,8 @@ static void choose_pixel_fmt(AVStream *st, AVCodec *codec)
 {
     if(codec && codec->pix_fmts){
         const enum PixelFormat *p= codec->pix_fmts;
+        int has_alpha= av_pix_fmt_descriptors[st->codec->pix_fmt].nb_components % 2 == 0;
+        enum PixelFormat best= PIX_FMT_NONE;
         if(st->codec->strict_std_compliance <= FF_COMPLIANCE_UNOFFICIAL){
             if(st->codec->codec_id==CODEC_ID_MJPEG){
                 p= (const enum PixelFormat[]){PIX_FMT_YUVJ420P, PIX_FMT_YUVJ422P, PIX_FMT_YUV420P, PIX_FMT_YUV422P, PIX_FMT_NONE};
@@ -772,6 +774,7 @@ static void choose_pixel_fmt(AVStream *st, AVCodec *codec)
             }
         }
         for (; *p != PIX_FMT_NONE; p++) {
+            best= avcodec_find_best_pix_fmt2(best, *p, st->codec->pix_fmt, has_alpha, NULL);
             if(*p == st->codec->pix_fmt)
                 break;
         }
@@ -781,8 +784,8 @@ static void choose_pixel_fmt(AVStream *st, AVCodec *codec)
                         "Incompatible pixel format '%s' for codec '%s', auto-selecting format '%s'\n",
                         av_pix_fmt_descriptors[st->codec->pix_fmt].name,
                         codec->name,
-                        av_pix_fmt_descriptors[codec->pix_fmts[0]].name);
-            st->codec->pix_fmt = codec->pix_fmts[0];
+                        av_pix_fmt_descriptors[best].name);
+            st->codec->pix_fmt = best;
         }
     }
 }