ffplay: add page (#7270)

* ffplay: add page

* backtick

* Update pages/common/ffplay.md

Co-authored-by: Muhammad Falak R Wani <falakreyaz@gmail.com>

Co-authored-by: Muhammad Falak R Wani <falakreyaz@gmail.com>

pages/common/ffplay.md

@@ -0,0 +1,16 @@
+# ffplay
+
+> A simple and portable media player using the FFmpeg libraries and the SDL library.
+> More information: <https://ffmpeg.org/ffplay-all.html>.
+
+- Play a media file:
+
+`ffplay {{path/to/file}}`
+
+- Play a video and show motion vectors in real time:
+
+`ffplay -flags2 +export_mvs -vf codecview=mv=pf+bf+bb {{path/to/file}}`
+
+- Show only video keyframes:
+
+`ffplay -vf select="{{eq(pict_type\,PICT_TYPE_I)}}" {{path/to/file}}`