From a30c4d9551863065a0c9c15601a5647341efef0f Mon Sep 17 00:00:00 2001
From: Isaac Connor <iconnor@connortechnology.com>
Date: Thu, 21 Mar 2019 10:41:59 -0400
Subject: [PATCH] rework ffmpeg_input to not use pkt_duration which doesn't
 exist in avconv

---
 src/zm_ffmpeg_input.cpp | 47 +++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 21 deletions(-)

diff --git a/src/zm_ffmpeg_input.cpp b/src/zm_ffmpeg_input.cpp
index d9c7c2fd3..139e6d862 100644
--- a/src/zm_ffmpeg_input.cpp
+++ b/src/zm_ffmpeg_input.cpp
@@ -214,39 +214,44 @@ AVFrame *FFmpeg_Input::get_frame( int stream_id, double at ) {
   seek_target = av_rescale_q(seek_target, AV_TIME_BASE_Q, input_format_context->streams[stream_id]->time_base);
   Debug(1, "Getting frame from stream %d at %" PRId64, stream_id, seek_target);
 
-  if ( frame ) {
-    if ( (frame->pts + frame->pkt_duration) > seek_target ) {
-      // The current frame is still the valid picture.
-      Debug(2,"Returning previous frame which is still good");
-      return frame;
-    }
-    if ( frame->pts < seek_target  ) {
-      Debug(2, "Frame pts %" PRId64 " duration %" PRId64, frame->pts, frame->pkt_duration);
-      while ( frame && (frame->pts < seek_target) ) {
-        if ( ! get_frame(stream_id) ) 
-          return frame;
-      }
-      return frame;
-    }
-  }
-
   int ret;
-  if ( frame ) {
-    if ( ( ret = av_seek_frame(input_format_context, stream_id, seek_target, AVSEEK_FLAG_ANY) < 0 ) ) {
+
+  if ( !frame ) {
+    // Don't have a frame yet, so get a keyframe before the timestamp
+    if ( ( ret = av_seek_frame(
+            input_format_context, stream_id, seek_target, AVSEEK_FLAG_FRAME
+            ) < 0 ) ) {
       Error("Unable to seek in stream");
       return NULL;
     }
+    // Have to grab a frame to update our current frame to know where we are
+    get_frame(stream_id);
+  } // end if ! frame
 
-  } else {
-    // No previous frame... are we asking for first frame?
-    // Must go for a keyframe
+  if ( frame->pts > seek_target ) {
+    zm_dump_frame(frame, "frame->pts > seek_target, seek backwards");
+  // our frame must be beyond our seek target. so go backwards to before it
     if ( ( ret = av_seek_frame(input_format_context, stream_id, seek_target, 
             AVSEEK_FLAG_BACKWARD | AVSEEK_FLAG_FRAME
             ) < 0 ) ) {
       Error("Unable to seek in stream");
       return NULL;
     }
+    // Have to grab a frame to update our current frame to know where we are
+    get_frame(stream_id);
+    zm_dump_frame(frame, "frame->pts > seek_target, got");
+  } // end if frame->pts > seek_target
+
+  // Seeking seems to typically seek to a keyframe, so then we have to decode until we get the frame we want.
+  if ( frame->pts <= seek_target  ) {
+    zm_dump_frame(frame, "pts <= seek_target");
+    while ( frame && (frame->pts < seek_target) ) {
+      if ( ! get_frame(stream_id) ) 
+        return frame;
+    }
+    return frame;
   }
+
   return get_frame(stream_id);
 
 } // end AVFrame *FFmpeg_Input::get_frame( int stream_id, struct timeval at)