Support gray8a pam encoding.

libavcodec/pamenc.c

@@ -62,6 +62,12 @@ static int pam_encode_frame(AVCodecContext *avctx, unsigned char *outbuf,
         maxval     = 255;
         tuple_type = "GRAYSCALE";
         break;
+    case PIX_FMT_GRAY8A:
+        n          = w * 2;
+        depth      = 2;
+        maxval     = 255;
+        tuple_type = "GRAYSCALE_ALPHA";
+        break;
     case PIX_FMT_RGB24:
         n          = w * 3;
         depth      = 3;
@@ -122,6 +128,6 @@ AVCodec ff_pam_encoder = {
     .priv_data_size = sizeof(PNMContext),
     .init           = ff_pnm_init,
     .encode         = pam_encode_frame,
-    .pix_fmts  = (const enum PixelFormat[]){PIX_FMT_RGB24, PIX_FMT_RGB32, PIX_FMT_GRAY8, PIX_FMT_MONOBLACK, PIX_FMT_NONE},
+    .pix_fmts  = (const enum PixelFormat[]){PIX_FMT_RGB24, PIX_FMT_RGB32, PIX_FMT_GRAY8, PIX_FMT_GRAY8A, PIX_FMT_MONOBLACK, PIX_FMT_NONE},
     .long_name = NULL_IF_CONFIG_SMALL("PAM (Portable AnyMap) image"),
 };