fftools/ffmpeg: use a separate variable for discontinuity offset

This will allow to move normal offset handling to demuxer thread, since
discontinuities currently have to be processed in the main thread, as
the code uses some decoder-produced values.

fftools/ffmpeg.c

@@ -3694,8 +3694,8 @@ static void decode_flush(InputFile *ifile)
     }
 }
 
-static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
-                                     AVPacket *pkt)
+static void ts_discontinuity_detect(InputFile *ifile, InputStream *ist,
+                                    AVPacket *pkt)
 {
     const int fmt_is_discont = ifile->ctx->iformat->flags & AVFMT_TS_DISCONT;
     int disable_discontinuity_correction = copy_ts;
@@ -3716,13 +3716,13 @@ static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
         if (fmt_is_discont) {
             if (FFABS(delta) > 1LL * dts_delta_threshold * AV_TIME_BASE ||
                 pkt_dts + AV_TIME_BASE/10 < FFMAX(ist->pts, ist->dts)) {
-                ifile->ts_offset -= delta;
+                ifile->ts_offset_discont -= delta;
                 av_log(NULL, AV_LOG_DEBUG,
                        "timestamp discontinuity for stream #%d:%d "
                        "(id=%d, type=%s): %"PRId64", new offset= %"PRId64"\n",
                        ist->file_index, ist->st->index, ist->st->id,
                        av_get_media_type_string(ist->st->codecpar->codec_type),
-                       delta, ifile->ts_offset);
+                       delta, ifile->ts_offset_discont);
                 pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
                 if (pkt->pts != AV_NOPTS_VALUE)
                     pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
@@ -3745,10 +3745,10 @@ static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
                fmt_is_discont && ifile->last_ts != AV_NOPTS_VALUE) {
         int64_t delta = pkt_dts - ifile->last_ts;
         if (FFABS(delta) > 1LL * dts_delta_threshold * AV_TIME_BASE) {
-            ifile->ts_offset -= delta;
+            ifile->ts_offset_discont -= delta;
             av_log(NULL, AV_LOG_DEBUG,
                    "Inter stream timestamp discontinuity %"PRId64", new offset= %"PRId64"\n",
-                   delta, ifile->ts_offset);
+                   delta, ifile->ts_offset_discont);
             pkt->dts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
             if (pkt->pts != AV_NOPTS_VALUE)
                 pkt->pts -= av_rescale_q(delta, AV_TIME_BASE_Q, ist->st->time_base);
@@ -3758,6 +3758,26 @@ static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
     ifile->last_ts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);
 }
 
+static void ts_discontinuity_process(InputFile *ifile, InputStream *ist,
+                                     AVPacket *pkt)
+{
+    int64_t offset = av_rescale_q(ifile->ts_offset_discont, AV_TIME_BASE_Q,
+                                  ist->st->time_base);
+
+    // apply previously-detected timestamp-discontinuity offset
+    // (to all streams, not just audio/video)
+    if (pkt->dts != AV_NOPTS_VALUE)
+        pkt->dts += offset;
+    if (pkt->pts != AV_NOPTS_VALUE)
+        pkt->pts += offset;
+
+    // detect timestamp discontinuities for audio/video
+    if ((ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
+         ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) &&
+        pkt->dts != AV_NOPTS_VALUE)
+        ts_discontinuity_detect(ifile, ist, pkt);
+}
+
 /*
  * Return
  * - 0 -- one packet was read and processed
@@ -3898,11 +3918,8 @@ static int process_input(int file_index)
     if (pkt->dts != AV_NOPTS_VALUE)
         pkt->dts += duration;
 
-    // detect and correct timestamp discontinuities for audio/video
-    if ((ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO ||
-         ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO) &&
-        pkt->dts != AV_NOPTS_VALUE)
-        ts_discontinuity_process(ifile, ist, pkt);
+    // detect and try to correct for timestamp discontinuities
+    ts_discontinuity_process(ifile, ist, pkt);
 
     if (debug_ts) {
         av_log(NULL, AV_LOG_INFO, "demuxer+ffmpeg -> ist_index:%d type:%s pkt_pts:%s pkt_pts_time:%s pkt_dts:%s pkt_dts_time:%s duration:%s duration_time:%s off:%s off_time:%s\n",

fftools/ffmpeg.h

@@ -427,6 +427,10 @@ typedef struct InputFile {
     int input_sync_ref;
 
     int64_t ts_offset;
+    /**
+     * Extra timestamp offset added by discontinuity handling.
+     */
+    int64_t ts_offset_discont;
     int64_t last_ts;
     int64_t start_time;   /* user-specified start time in AV_TIME_BASE or AV_NOPTS_VALUE */
     int64_t recording_time;