libavfilter: add ff_parse_time_base()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/formats.c

@@ -21,6 +21,7 @@
 
 #include "libavutil/eval.h"
 #include "libavutil/pixdesc.h"
+#include "libavutil/parseutils.h"
 #include "libavutil/audioconvert.h"
 #include "avfilter.h"
 #include "internal.h"
@@ -493,6 +494,17 @@ int ff_parse_sample_format(int *ret, const char *arg, void *log_ctx)
     return 0;
 }
 
+int ff_parse_time_base(AVRational *ret, const char *arg, void *log_ctx)
+{
+    AVRational r;
+    if(av_parse_ratio(&r, arg, INT_MAX, 0, log_ctx) < 0 ||r.num<=0  ||r.den<=0) {
+        av_log(log_ctx, AV_LOG_ERROR, "Invalid time base '%s'\n", arg);
+        return AVERROR(EINVAL);
+    }
+    *ret = r;
+    return 0;
+}
+
 int ff_parse_sample_rate(int *ret, const char *arg, void *log_ctx)
 {
     char *tail;

libavfilter/internal.h

@@ -111,6 +111,16 @@ int ff_parse_pixel_format(enum PixelFormat *ret, const char *arg, void *log_ctx)
  */
 int ff_parse_sample_rate(int *ret, const char *arg, void *log_ctx);
 
+/**
+ * Parse a time base.
+ *
+ * @param ret unsigned AVRational pointer to where the value should be written
+ * @param arg string to parse
+ * @param log_ctx log context
+ * @return 0 in case of success, a negative AVERROR code on error
+ */
+int ff_parse_time_base(AVRational *ret, const char *arg, void *log_ctx);
+
 /**
  * Parse a sample format name or a corresponding integer representation.
  *