lavf/dashenc: pass standards compliance value to the internal context

Enables one to test possibly nonstandard formats such as Opus or
FLAC in ISOBMFF, among other things.

This becomes much more useful if output segment format becomes an
option, or if the WebM segment feature gets removed.

libavformat/dashenc.c

@@ -983,10 +983,11 @@ static int dash_init(AVFormatContext *s)
         if (!ctx->oformat)
             return AVERROR_MUXER_NOT_FOUND;
         os->ctx = ctx;
-        ctx->interrupt_callback = s->interrupt_callback;
-        ctx->opaque             = s->opaque;
-        ctx->io_close           = s->io_close;
-        ctx->io_open            = s->io_open;
+        ctx->interrupt_callback    = s->interrupt_callback;
+        ctx->opaque                = s->opaque;
+        ctx->io_close              = s->io_close;
+        ctx->io_open               = s->io_open;
+        ctx->strict_std_compliance = s->strict_std_compliance;
 
         if (!(st = avformat_new_stream(ctx, NULL)))
             return AVERROR(ENOMEM);