[RFC] examples/ola_recorder: mitigate against drifting playback offset

examples/ShowPlayer.cpp

@@ -31,6 +31,7 @@
 #include <ola/base/SysExits.h>
 #include <ola/client/ClientWrapper.h>
 #include <ola/client/OlaClient.h>
+#include <climits>
 #include <fstream>
 #include <iostream>
 #include <string>
@@ -216,15 +217,18 @@ ShowLoader::State ShowPlayer::SeekTo(uint64_t seek_time) {
       break;
     }
   }
+  uint64_t timeout = playhead_time - seek_time;
   m_playback_pos = playhead_time;
+  m_clock.CurrentMonotonicTime(&m_start_ts);
+  m_start_playback_pos = m_playback_pos - timeout;
 
   // Send data in the state it would be in at the given time
   map<unsigned int, ShowEntry>::iterator entry_it;
   for (entry_it = entries.begin(); entry_it != entries.end(); ++entry_it) {
     SendFrame(entry_it->second);
   }
   // Adjust the timeout to handle landing in the middle of the entry's timeout
-  RegisterNextTimeout(playhead_time-seek_time);
+  RegisterNextTimeout(timeout);
 
   return ShowLoader::OK;
 }
@@ -270,8 +274,35 @@ void ShowPlayer::SendEntry(const ShowEntry &entry) {
   SendFrame(entry);
   m_playback_pos += entry.next_wait;
 
+  unsigned int timeout = entry.next_wait;
+  if (!m_simulate) {
+    // Using int64_t for target_delta here because we have to lose 1 bit anyway
+    // as InMilliSeconds() returns a signed 64-bit integer.
+    ola::TimeStamp now;
+    m_clock.CurrentMonotonicTime(&now);
+    int64_t target_delta = m_playback_pos - m_start_playback_pos;
+    int64_t current_delta = (now - m_start_ts).InMilliSeconds();
+    int64_t delay = target_delta - current_delta;
+    if (delay < 0) {
+      OLA_WARN << "Frame at line " << m_loader.GetCurrentLineNumber()
+               << " was meant to have completed " << -delay << " ms ago."
+               << " System too slow?";
+      delay = 0;
+    }
+
+#if UINT_MAX < INT64_MAX
+    if (delay > UINT_MAX) {
+      OLA_WARN << "Calculated delay of " << delay << " ms"
+               << " exceeded maximum delay of " << UINT_MAX << " ms."
+               << " Clamping to maximum.";
+      delay = UINT_MAX;
+    }
+#endif
+
+    timeout = delay;
+  }
   // Set when next to send data
-  RegisterNextTimeout(entry.next_wait);
+  RegisterNextTimeout(timeout);
 }
 
 

examples/ShowPlayer.h

@@ -18,6 +18,7 @@
  * Copyright (C) 2011 Simon Newton
  */
 
+#include <ola/Clock.h>
 #include <ola/DmxBuffer.h>
 #include <ola/client/ClientWrapper.h>
 
@@ -89,6 +90,9 @@ class ShowPlayer {
   uint64_t m_run_time;
   std::map<unsigned int, uint64_t> m_frame_count;
   bool m_simulate;
+  ola::Clock m_clock;
+  ola::TimeStamp m_start_ts;
+  uint64_t m_start_playback_pos;
 
   /** Used for tracking simulation progress */
   typedef enum {

examples/ShowSaver.cpp

@@ -41,7 +41,8 @@ using std::endl;
 const char ShowSaver::OLA_SHOW_HEADER[] = "OLA Show";
 
 ShowSaver::ShowSaver(const string &filename)
-    : m_filename(filename) {
+    : m_filename(filename),
+      m_saved_elapsed_ms(0) {
 }
 
 
@@ -84,13 +85,17 @@ bool ShowSaver::NewFrame(const ola::TimeStamp &arrival_time,
                          unsigned int universe,
                          const ola::DmxBuffer &data) {
   // TODO(simon): add much better error handling here
-  if (m_last_frame.IsSet()) {
-    // this is not the first frame so write the delay in ms
-    const ola::TimeInterval delta = arrival_time - m_last_frame;
-
-    m_show_file << delta.InMilliSeconds() << endl;
+  if (m_first_frame.IsSet()) {
+    const ola::TimeInterval delta = arrival_time - m_first_frame;
+    int64_t saved_delta_ms = (delta.InMilliSeconds() - m_saved_elapsed_ms);
+    m_saved_elapsed_ms += saved_delta_ms;
+
+    m_show_file << saved_delta_ms << endl;
+  } else {
+    m_first_frame = arrival_time;
   }
-  m_last_frame = arrival_time;
+
   m_show_file << universe << " " << data.ToString() << endl;
+
   return true;
 }

examples/ShowSaver.h

@@ -45,7 +45,8 @@ class ShowSaver {
  private:
   const std::string m_filename;
   std::ofstream m_show_file;
-  ola::TimeStamp m_last_frame;
+  ola::TimeStamp m_first_frame;
+  int64_t m_saved_elapsed_ms;
 
   static const char OLA_SHOW_HEADER[];
 };