time_base description by Rich Felker | dalias, aerifal cx

Originally committed as revision 4536 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/avcodec.h

@@ -732,14 +732,17 @@ typedef struct AVCodecContext {
     void *extradata;
     int extradata_size;
     
-    /* video only */
     /**
-     * time base in which the timestamps are specified.
+     * this is the fundamental unit of time (in seconds) in terms
+     * of which frame timestamps are represented. for fixed-fps content,
+     * timebase should be 1/framerate and timestamp increments should be
+     * identically 1.
      * - encoding: MUST be set by user
      * - decoding: set by lavc.
      */
     AVRational time_base;
     
+    /* video only */
     /**
      * picture width / height.
      * - encoding: MUST be set by user. 

libavformat/avformat.h

@@ -229,6 +229,13 @@ typedef struct AVStream {
     int codec_info_nb_frames;
     /* encoding: PTS generation when outputing stream */
     AVFrac pts;
+
+    /**
+     * this is the fundamental unit of time (in seconds) in terms
+     * of which frame timestamps are represented. for fixed-fps content,
+     * timebase should be 1/framerate and timestamp increments should be
+     * identically 1.
+     */
     AVRational time_base;
     int pts_wrap_bits; /* number of bits in pts (used for wrapping control) */
     /* ffmpeg.c private use */

output_example.c

@@ -199,7 +199,10 @@ AVStream *add_video_stream(AVFormatContext *oc, int codec_id)
     /* resolution must be a multiple of two */
     c->width = 352;  
     c->height = 288;
-    /* frames per second */
+    /* time base: this is the fundamental unit of time (in seconds) in terms
+       of which frame timestamps are represented. for fixed-fps content,
+       timebase should be 1/framerate and timestamp increments should be
+       identically 1. */
     c->time_base.den = STREAM_FRAME_RATE;  
     c->time_base.num = 1;
     c->gop_size = 12; /* emit one intra frame every twelve frames at most */