Do not set the codec's pixel format in the format's write_header()

Originally committed as revision 5887 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/gif.c

@@ -339,8 +339,10 @@ static int gif_write_header(AVFormatContext *s)
 //        rate = video_enc->time_base.den;
     }
 
-    /* XXX: is it allowed ? seems to work so far... */
-    video_enc->pix_fmt = PIX_FMT_RGB24;
+    if (video_enc->pix_fmt != PIX_FMT_RGB24) {
+        av_log(s, AV_LOG_ERROR, "ERROR: gif only handles the rgb24 pixel format. Use -pix_fmt rgb24.\n");
+        return AVERROR_IO;
+    }
 
     gif_image_write_header(pb, width, height, loop_count, NULL);
 

tests/regression.sh

@@ -691,7 +691,7 @@ do_ffmpeg_crc $file -f image2pipe -i $file
 
 # gif
 file=${outfile}libav.gif
-do_ffmpeg $file -t 1 -y -qscale 10 -f pgmyuv -i $raw_src $file
+do_ffmpeg $file -t 1 -y -qscale 10 -f pgmyuv -i $raw_src -pix_fmt rgb24 $file
 #do_ffmpeg_crc $file -i $file
 
 # yuv4mpeg