almost complete implementation

format_cb.c

@@ -0,0 +1,11 @@
+#include <libavcodec/avcodec.h>
+#include <libavutil/pixfmt.h>
+
+enum AVPixelFormat get_sw_format(AVCodecContext *ctx, const enum AVPixelFormat *pix_fmts) {
+    for (const enum AVPixelFormat *p = pix_fmts; *p != AV_PIX_FMT_NONE; p++) {
+        if (*p == AV_PIX_FMT_YUV420P || *p == AV_PIX_FMT_YUV420P10LE) {
+            return *p;
+        }
+    }
+    return pix_fmts[0];
+}