[FFmpeg-devel] [PATCH 1/2] avdevice/decklink_dec: mark the field flag if framerate > 30FPS

[lance.lmwang at gmail.com]

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

In SMPTE ST 12-1: 2014 Sec 12.2, we need to mark the frame flag if the frame rate > 30FPS to
avoid interoperability issues. It will be used by the encoder to identify even or odd frames
and correctly calculate the frame number of the SEI TC.

---
 libavdevice/decklink_common.h |  1 +
 libavdevice/decklink_dec.cpp  | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/libavdevice/decklink_common.h b/libavdevice/decklink_common.h
index bd68c7b..8ddc411 100644
--- a/libavdevice/decklink_common.h
+++ b/libavdevice/decklink_common.h
@@ -151,6 +151,7 @@ struct decklink_ctx {
     int channels;
     int audio_depth;
     unsigned long tc_seen;    // used with option wait_for_tc
+    uint32_t last_tc;
 };
 
 typedef enum { DIRECTION_IN, DIRECTION_OUT} decklink_direction_t;
diff --git a/libavdevice/decklink_dec.cpp b/libavdevice/decklink_dec.cpp
index dde68ff..a60c01b 100644
--- a/libavdevice/decklink_dec.cpp
+++ b/libavdevice/decklink_dec.cpp
@@ -884,12 +884,26 @@ HRESULT decklink_input_callback::VideoInputFrameArrived(
                         int metadata_len;
                         uint8_t* packed_metadata;
                         AVTimecode tcr;
+                        AVRational rate = ctx->video_st->r_frame_rate;
 
                         if (av_timecode_init_from_string(&tcr, ctx->video_st->r_frame_rate, tc, ctx) >= 0) {
                             uint32_t tc_data = av_timecode_get_smpte_from_framenum(&tcr, 0);
                             int size = sizeof(uint32_t) * 4;
                             uint32_t *sd = (uint32_t *)av_packet_new_side_data(&pkt, AV_PKT_DATA_S12M_TIMECODE, size);
 
+                            /* set the field flag if frame rate > 30FPS */
+                            /* Refer to SMPTE ST 12-1:2014 Sec 12.2 */
+                            if (av_cmp_q(rate, (AVRational) {30, 1}) == 1) {
+                                /* Odd frame */
+                                if (ctx->last_tc == tc_data) {
+                                    if (av_cmp_q(rate, (AVRational) {50, 1}) == 0)
+                                        tc_data |= (1 << 7);
+                                    else
+                                        tc_data |= (1 << 23);
+                                }
+                            }
+                            ctx->last_tc = tc_data;
+
                             if (sd) {
                                 *sd       = 1;       // one TC
                                 *(sd + 1) = tc_data; // TC
-- 
2.9.4