proresenc_ks: allow auto-selecting profile

The user may not know how to select the profile, nor what he needs, in
particular to encode alpha.

Therefore, use an automatic selection as default, and warn when the
manually selected profile may cause issues.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/proresenc_kostya.c

@@ -40,6 +40,7 @@
 #define MAX_PLANES 4
 
 enum {
+    PRORES_PROFILE_AUTO  = -1,
     PRORES_PROFILE_PROXY = 0,
     PRORES_PROFILE_LT,
     PRORES_PROFILE_STANDARD,
@@ -1146,7 +1147,21 @@ static av_cold int encode_init(AVCodecContext *avctx)
                "there should be an integer power of two MBs per slice\n");
         return AVERROR(EINVAL);
     }
+    if (ctx->profile == PRORES_PROFILE_AUTO) {
+        ctx->profile = av_pix_fmt_desc_get(avctx->pix_fmt)->flags & AV_PIX_FMT_FLAG_ALPHA
+                     ? PRORES_PROFILE_4444 : PRORES_PROFILE_HQ;
+        av_log(avctx, AV_LOG_INFO, "Autoselected %s. It can be overridden "
+               "through -profile option.\n", ctx->profile == PRORES_PROFILE_4444
+               ? "4:4:4:4 profile because of the alpha channel"
+               : "HQ profile to keep best quality");
+    }
     if (av_pix_fmt_desc_get(avctx->pix_fmt)->flags & AV_PIX_FMT_FLAG_ALPHA) {
+        if (ctx->profile != PRORES_PROFILE_4444) {
+            // force alpha and warn
+            av_log(avctx, AV_LOG_WARNING, "Profile selected will not "
+                   "encode alpha. Override with -profile if needed.\n");
+            ctx->alpha_bits = 0;
+        }
         if (ctx->alpha_bits & 7) {
             av_log(avctx, AV_LOG_ERROR, "alpha bits should be 0, 8 or 16\n");
             return AVERROR(EINVAL);
@@ -1280,8 +1295,10 @@ static const AVOption options[] = {
     { "mbs_per_slice", "macroblocks per slice", OFFSET(mbs_per_slice),
         AV_OPT_TYPE_INT, { .i64 = 8 }, 1, MAX_MBS_PER_SLICE, VE },
     { "profile",       NULL, OFFSET(profile), AV_OPT_TYPE_INT,
-        { .i64 = PRORES_PROFILE_STANDARD },
-        PRORES_PROFILE_PROXY, PRORES_PROFILE_4444, VE, "profile" },
+        { .i64 = PRORES_PROFILE_AUTO },
+        PRORES_PROFILE_AUTO, PRORES_PROFILE_4444, VE, "profile" },
+    { "auto",         NULL, 0, AV_OPT_TYPE_CONST, { .i64 = PRORES_PROFILE_AUTO },
+        0, 0, VE, "profile" },
     { "proxy",         NULL, 0, AV_OPT_TYPE_CONST, { .i64 = PRORES_PROFILE_PROXY },
         0, 0, VE, "profile" },
     { "lt",            NULL, 0, AV_OPT_TYPE_CONST, { .i64 = PRORES_PROFILE_LT },