[FFmpeg-devel] [PATCH v4 1/2] avutil/timecode: add description for SMPTE binary format

[lance.lmwang at gmail.com]

From: Limin Wang <lance.lmwang at gmail.com>

AV_FRAME_DATA_S12M_TIMECODE is public API, so user need to know its format
by the API header instead of reading the code.

Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
---
 libavutil/frame.h    |  4 ++--
 libavutil/timecode.h | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/libavutil/frame.h b/libavutil/frame.h
index 3fb8c56..c694b12 100644
--- a/libavutil/frame.h
+++ b/libavutil/frame.h
@@ -162,8 +162,8 @@ enum AVFrameSideDataType {
     /**
      * Timecode which conforms to SMPTE ST 12-1. The data is an array of 4 uint32_t
      * where the first uint32_t describes how many (1-3) of the other timecodes are used.
-     * The timecode format is described in the av_timecode_get_smpte_from_framenum()
-     * function in libavutil/timecode.c.
+     * The timecode format is described in the comments of av_timecode_get_smpte_from_framenum()
+     * function in libavutil/timecode.h.
      */
     AV_FRAME_DATA_S12M_TIMECODE,
 
diff --git a/libavutil/timecode.h b/libavutil/timecode.h
index ab38e66..b1c1887 100644
--- a/libavutil/timecode.h
+++ b/libavutil/timecode.h
@@ -61,7 +61,21 @@ int av_timecode_adjust_ntsc_framenum2(int framenum, int fps);
  * @param tc       timecode data correctly initialized
  * @param framenum frame number
  * @return         the SMPTE binary representation
- *
+ * the format description as follows, note it's in system byte order:
+ * 31b:     color frame flag (0: unsync mode, 1: sync mode)
+ * 30b:     drop  frame flag (0: non drop,    1: drop)
+ * 28b,29b: tens  of frames
+ * 24-27b:  units of frames
+ * 23b:     PC (NTSC) or BGF0 (PAL)
+ * 20b,22b: tens  of seconds
+ * 16-19b:  units of seconds
+ * 15b:     BGF0 (NTSC) or BGF2 (PAL)
+ * 12b,13b: tens  of minutes
+ * 8-11b:   units of minutes
+ * 7b:      BGF2 (NTSC) or PC (PAL)
+ * 6b:      BGF1
+ * 4b,5b:   tens  of hours
+ * 0b-3b:   units of hours
  * @note Frame number adjustment is automatically done in case of drop timecode,
  *       you do NOT have to call av_timecode_adjust_ntsc_framenum2().
  * @note The frame number is relative to tc->start.
-- 
1.8.3.1