mux/nut: factorize ff_choose_timebase() out of nut

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

libavformat/internal.h

@@ -354,5 +354,13 @@ void ff_compute_frame_duration(int *pnum, int *pden, AVStream *st,
 
 int ff_get_audio_frame_size(AVCodecContext *enc, int size, int mux);
 
+/**
+ * Chooses a timebase for muxing the specified stream.
+ *
+ * The choosen timebase allows sample accurate timestamps based
+ * on the framerate or sample rate for audio streams. It also is
+ * at least as precisse as 1/min_precission would be.
+ */
+AVRational ff_choose_timebase(AVFormatContext *s, AVStream *st, int min_precission);
 
 #endif /* AVFORMAT_INTERNAL_H */

libavformat/mux.c

@@ -103,6 +103,25 @@ static void frac_add(AVFrac *f, int64_t incr)
     f->num = num;
 }
 
+AVRational ff_choose_timebase(AVFormatContext *s, AVStream *st, int min_precission)
+{
+    AVRational q;
+    int j;
+
+    if (st->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
+        q = (AVRational){1, st->codec->sample_rate};
+    } else {
+        q = st->codec->time_base;
+    }
+    for (j=2; j<2000; j+= 1+(j>2))
+        while (q.den / q.num < min_precission && q.num % j == 0)
+            q.num /= j;
+    while (q.den / q.num < min_precission && q.den < (1<<24))
+        q.den <<= 1;
+
+    return q;
+}
+
 int avformat_alloc_output_context2(AVFormatContext **avctx, AVOutputFormat *oformat,
                                    const char *format, const char *filename)
 {

libavformat/nutenc.c

@@ -676,11 +676,7 @@ static int nut_write_header(AVFormatContext *s){
         if(st->codec->codec_type == AVMEDIA_TYPE_AUDIO && st->codec->sample_rate) {
             time_base = (AVRational){1, st->codec->sample_rate};
         } else {
-            for (j=2; j<2000; j+= 1+(j>2))
-                while (time_base.den / time_base.num < 48000 && time_base.num % j == 0)
-                    time_base.num /= j;
-            while (time_base.den / time_base.num < 48000 && time_base.den < (1<<24))
-                time_base.den <<= 1;
+            time_base = ff_choose_timebase(s, st, 48000);
         }
 
         avpriv_set_pts_info(st, 64, time_base.num, time_base.den);