x264: Add option to force IDR frames

When forwarding the frame type information, by default x264 can
decide which kind of keyframe output, add an option to force it
to output IDR frames in to support use-cases such as preparing
the content for segmented streams formats.

libavcodec/libx264.c

@@ -77,6 +77,7 @@ typedef struct X264Context {
     char *stats;
     int nal_hrd;
     int motion_est;
+    int forced_idr;
     char *x264_params;
 } X264Context;
 
@@ -235,11 +236,22 @@ static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame,
         }
 
         x4->pic.i_pts  = frame->pts;
-        x4->pic.i_type =
-            frame->pict_type == AV_PICTURE_TYPE_I ? X264_TYPE_KEYFRAME :
-            frame->pict_type == AV_PICTURE_TYPE_P ? X264_TYPE_P :
-            frame->pict_type == AV_PICTURE_TYPE_B ? X264_TYPE_B :
-                                            X264_TYPE_AUTO;
+
+        switch (frame->pict_type) {
+        case AV_PICTURE_TYPE_I:
+            x4->pic.i_type = x4->forced_idr ? X264_TYPE_IDR
+                                            : X264_TYPE_KEYFRAME;
+            break;
+        case AV_PICTURE_TYPE_P:
+            x4->pic.i_type = X264_TYPE_P;
+            break;
+        case AV_PICTURE_TYPE_B:
+            x4->pic.i_type = X264_TYPE_B;
+            break;
+        default:
+            x4->pic.i_type = X264_TYPE_AUTO;
+            break;
+        }
         reconfig_encoder(ctx, frame);
     }
     do {
@@ -696,6 +708,7 @@ static const AVOption options[] = {
     { "umh",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_UMH },  INT_MIN, INT_MAX, VE, "motion-est" },
     { "esa",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_ESA },  INT_MIN, INT_MAX, VE, "motion-est" },
     { "tesa",          NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_TESA }, INT_MIN, INT_MAX, VE, "motion-est" },
+    { "forced-idr",   "If forwarding iframes, require them to be IDR frames.", OFFSET(forced_idr),  AV_OPT_TYPE_INT,    { .i64 = 0 }, 0, 1, VE },
     { "x264-params",  "Override the x264 configuration using a :-separated list of key=value parameters", OFFSET(x264_params), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE },
     { NULL },
 };