ffmpeg: set muxer packet duration based on framerate only for CFR

a set ost->frame_rate does not imply CFR in ffmpeg

The changed fate tests had all wrong packet durations
(like 1/1000 or 1/90000)

There might be more cases in which is_cfr could be set

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

1 files changed, 1 insertions, 0 deletions

diff --git a/ffmpeg.h b/ffmpeg.h
index cdcb3b46fa..39b9edab52 100644
--- a/ffmpeg.h
+++ b/ffmpeg.h
@@ -421,6 +421,7 @@ typedef struct OutputStream {
 
     /* video only */
     AVRational frame_rate;
+    int is_cfr;
     int force_fps;
     int top_field_first;
     int rotate_overridden;