png: make .long_name more descriptive

Signed-off-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Diego Biurrun <diego@biurrun.de>

libavcodec/pngdec.c

@@ -665,5 +665,5 @@ AVCodec ff_png_decoder = {
     .close          = png_dec_end,
     .decode         = decode_frame,
     .capabilities   = CODEC_CAP_DR1 /*| CODEC_CAP_DRAW_HORIZ_BAND*/,
-    .long_name = NULL_IF_CONFIG_SMALL("PNG image"),
+    .long_name = NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
 };

libavcodec/pngenc.c

@@ -457,5 +457,5 @@ AVCodec ff_png_encoder = {
     .init           = png_enc_init,
     .encode2        = encode_frame,
     .pix_fmts= (const enum PixelFormat[]){PIX_FMT_RGB24, PIX_FMT_RGB32, PIX_FMT_PAL8, PIX_FMT_GRAY8, PIX_FMT_MONOBLACK, PIX_FMT_NONE},
-    .long_name= NULL_IF_CONFIG_SMALL("PNG image"),
+    .long_name= NULL_IF_CONFIG_SMALL("PNG (Portable Network Graphics) image"),
 };