img2: add j2c file extension

Some applications use the j2c extension for jpeg2000 codestream files.

libavformat/img2.c

@@ -63,6 +63,7 @@ static const IdStrMap img_tags[] = {
     { AV_CODEC_ID_SUNRAST,    "im8"      },
     { AV_CODEC_ID_SUNRAST,    "im24"     },
     { AV_CODEC_ID_SUNRAST,    "sunras"   },
+    { AV_CODEC_ID_JPEG2000,   "j2c"      },
     { AV_CODEC_ID_JPEG2000,   "jp2"      },
     { AV_CODEC_ID_JPEG2000,   "jpc"      },
     { AV_CODEC_ID_JPEG2000,   "j2k"      },

libavformat/img2enc.c

@@ -148,7 +148,7 @@ AVOutputFormat ff_image2_muxer = {
     .long_name      = NULL_IF_CONFIG_SMALL("image2 sequence"),
     .extensions     = "bmp,dpx,jpeg,jpg,ljpg,pam,pbm,pcx,pgm,pgmyuv,png,"
                       "ppm,sgi,tga,tif,tiff,jp2,xwd,sun,ras,rs,im1,im8,im24,"
-                      "sunras,webp,xbm",
+                      "sunras,webp,xbm,j2c",
     .priv_data_size = sizeof(VideoMuxData),
     .video_codec    = AV_CODEC_ID_MJPEG,
     .write_header   = write_header,