caption_frame_decode: rework API

Fixes szatmary#59

* pop_on mode requires incrementing the frame timestamp until
  end_of_caption is encountered.

* caption_frame_decode now always updates the timestamp of the
  frame when the timestamp parameter != -1. This requires that callers
  only pass a valid timestamp when a new one is encountered, for
  example with SCC the timestamp at the start of the cue, then -1
  until the next new timestamp.

* A new enum member is added for the return value, LIBCAPTION_CLEAR.
  It allows the caller to determine that closed captions should not
  be displayed anymore, in order to finish the previous cue earlier
  than the start of the next cue.

caption/caption.h

@@ -43,7 +43,8 @@ typedef signed int ssize_t;
 typedef enum {
     LIBCAPTION_ERROR = 0,
     LIBCAPTION_OK = 1,
-    LIBCAPTION_READY = 2
+    LIBCAPTION_READY = 2,
+    LIBCAPTION_CLEAR = 3,
 } libcaption_stauts_t;
 
 static inline libcaption_stauts_t libcaption_status_update(libcaption_stauts_t old_stat, libcaption_stauts_t new_stat)

caption/srt.h

@@ -68,6 +68,8 @@ static inline utf8_char_t* srt_cue_data(srt_cue_t* cue) { return vtt_block_data(
 */
 static inline srt_cue_t* srt_cue_from_caption_frame(caption_frame_t* frame, srt_t* srt) { return vtt_cue_from_caption_frame(frame, srt); };
 
+static inline void srt_cue_finish(caption_frame_t* frame, srt_t* srt) { return vtt_cue_finish(frame, srt); };
+
 /*! \brief
     \param
 */

caption/vtt.h

@@ -134,6 +134,10 @@ int vtt_cue_to_caption_frame(vtt_block_t* cue, caption_frame_t* frame);
     \param
 */
 vtt_block_t* vtt_cue_from_caption_frame(caption_frame_t* frame, vtt_t* vtt);
+
+// finishes the last cue
+void vtt_cue_finish(caption_frame_t* frame, vtt_t* vtt);
+
 /*! \brief
     \param
 */

examples/scc2srt.c

@@ -42,11 +42,23 @@ int main(int argc, char** argv)
     scc_data += scc_to_608(&scc, scc_data);
 
     while (scc->cc_size) {
+        double timestamp = scc->timestamp;
+
         for (i = 0; i < scc->cc_size; ++i) {
             // eia608_dump (scc->cc_data[i]);
-            if (LIBCAPTION_READY == caption_frame_decode(&frame, scc->cc_data[i], scc->timestamp)) {
+
+            switch (caption_frame_decode(&frame, scc->cc_data[i], timestamp)) {
+            case LIBCAPTION_READY:
                 srt_cue_from_caption_frame(&frame, srt);
+                break;
+            case LIBCAPTION_CLEAR:
+                srt_cue_finish(&frame, srt);
+                break;
+            default:
+                break;
             }
+
+            timestamp = -1;
         }
 
         scc_data += scc_to_608(&scc, scc_data);

examples/scc2vtt.c

@@ -47,10 +47,22 @@ int main(int argc, char** argv)
     scc_data += scc_to_608(&scc, scc_data);
 
     while (scc->cc_size) {
+        double timestamp = scc->timestamp;
+
         for (i = 0; i < scc->cc_size; ++i) {
-            if (LIBCAPTION_READY == caption_frame_decode(&frame, scc->cc_data[i], scc->timestamp)) {
+
+            switch (caption_frame_decode(&frame, scc->cc_data[i], timestamp)) {
+            case LIBCAPTION_READY:
                 vtt_cue_from_caption_frame(&frame, vtt);
+                break;
+            case LIBCAPTION_CLEAR:
+                vtt_cue_finish(&frame, vtt);
+                break;
+            default:
+                break;
             }
+
+            timestamp = -1;
         }
 
         scc_data += scc_to_608(&scc, scc_data);

examples/sccdump.c

@@ -39,13 +39,21 @@ int main(int argc, char** argv)
     scc_data += scc_to_608(&scc, scc_data);
 
     while (scc->cc_size) {
-        fprintf(stderr, "Timestamp: %f\n", scc->timestamp);
+        double timestamp = scc->timestamp;
+
+        fprintf(stderr, "Timestamp: %f\n", timestamp);
 
         for (i = 0; i < scc->cc_size; ++i) {
             eia608_dump(scc->cc_data[i]);
-            if (LIBCAPTION_READY == caption_frame_decode(&frame, scc->cc_data[i], scc->timestamp)) {
+            switch (caption_frame_decode(&frame, scc->cc_data[i], timestamp)) {
+            case LIBCAPTION_READY:
                 caption_frame_dump(&frame);
+                break;
+            default:
+                break;
             }
+
+            timestamp = -1;
         }
 
         scc_data += scc_to_608(&scc, scc_data);

src/caption.c

@@ -214,7 +214,7 @@ libcaption_stauts_t caption_frame_decode_control(caption_frame_t* frame, uint16_
 
     case eia608_control_erase_display_memory:
         caption_frame_buffer_clear(&frame->front);
-        return LIBCAPTION_READY;
+        return LIBCAPTION_CLEAR;
 
     // ROLL-UP
     case eia608_control_roll_up_2:
@@ -306,17 +306,21 @@ libcaption_stauts_t caption_frame_decode(caption_frame_t* frame, uint16_t cc_dat
         return frame->status;
     }
 
-    if (0 > frame->timestamp || frame->timestamp == timestamp || LIBCAPTION_READY == frame->status) {
-        frame->timestamp = timestamp;
-        frame->status = LIBCAPTION_OK;
-    }
-
     // skip duplicate controll commands. We also skip duplicate specialna to match the behaviour of iOS/vlc
     if ((eia608_is_specialna(cc_data) || eia608_is_control(cc_data)) && cc_data == frame->state.cc_data) {
+        if (caption_frame_popon (frame))
+          frame->timestamp += (1 / 29.97);
+        return LIBCAPTION_OK;
+    }
+
+    if (timestamp >= 0) {
+        frame->timestamp = timestamp;
         frame->status = LIBCAPTION_OK;
-        return frame->status;
     }
 
+    if (caption_frame_popon (frame))
+      frame->timestamp += (1 / 29.97);
+
     frame->state.cc_data = cc_data;
 
     if (frame->xds.state) {

src/cea708.c

@@ -268,13 +268,16 @@ libcaption_stauts_t cea708_to_caption_frame(caption_frame_t* frame, cea708_t* ce
     libcaption_stauts_t status = LIBCAPTION_OK;
 
     if (GA94 == cea708->user_identifier) {
+        float timestamp = cea708->timestamp;
+
         for (i = 0; i < count; ++i) {
             int valid;
             cea708_cc_type_t type;
             uint16_t cc_data = cea708_cc_data(&cea708->user_data, i, &valid, &type);
 
             if (valid && cc_type_ntsc_cc_field_1 == type) {
-                status = libcaption_status_update(status, caption_frame_decode(frame, cc_data, cea708->timestamp));
+                status = libcaption_status_update(status, caption_frame_decode(frame, cc_data, timestamp));
+                timestamp = -1;
             }
         }
     }

src/vtt.c

@@ -316,6 +316,13 @@ vtt_block_t* vtt_cue_from_caption_frame(caption_frame_t* frame, vtt_t* vtt)
     return cue;
 }
 
+void vtt_cue_finish(caption_frame_t* frame, vtt_t* vtt)
+{
+    if (vtt->cue_tail && 0 >= vtt->cue_tail->duration) {
+        vtt->cue_tail->duration = frame->timestamp - vtt->cue_tail->timestamp;
+    }
+}
+
 static void _dump(vtt_t* vtt)
 {
     vtt_block_t* block;