Add gapless playback support for NuPlayer

This makes NuPlayer use a SkipCutBuffer when needed, and adds a new
AudioSink method to retrieve the number of frames written so far, so
NuPlayerRenderer can calculate how much data it can write without blocking.
Also make some more methods const.

Change-Id: Id7d253ad8a7b85e9a84ca2baafbe32817b16c744
diff --git a/libvideoeditor/lvpp/VideoEditorPlayer.cpp b/libvideoeditor/lvpp/VideoEditorPlayer.cpp
index 57cab08..1ba1f44 100755
--- a/libvideoeditor/lvpp/VideoEditorPlayer.cpp
+++ b/libvideoeditor/lvpp/VideoEditorPlayer.cpp
@@ -376,12 +376,19 @@
     return mMsecsPerFrame;
 }
 
-status_t VideoEditorPlayer::VeAudioOutput::getPosition(uint32_t *position) {
+status_t VideoEditorPlayer::VeAudioOutput::getPosition(uint32_t *position) const {
 
     if (mTrack == 0) return NO_INIT;
     return mTrack->getPosition(position);
 }
 
+status_t VideoEditorPlayer::VeAudioOutput::getFramesWritten(uint32_t *written) const {
+
+    if (mTrack == 0) return NO_INIT;
+    *written = mNumFramesWritten;
+    return OK;
+}
+
 status_t VideoEditorPlayer::VeAudioOutput::open(
         uint32_t sampleRate, int channelCount, audio_channel_mask_t channelMask,
         audio_format_t format, int bufferCount,
@@ -569,7 +576,7 @@
     return NO_ERROR;
 }
 
-int VideoEditorPlayer::VeAudioOutput::getSessionId() {
+int VideoEditorPlayer::VeAudioOutput::getSessionId() const {
 
     return mSessionId;
 }
diff --git a/libvideoeditor/lvpp/VideoEditorPlayer.h b/libvideoeditor/lvpp/VideoEditorPlayer.h
index 6962501..350b384 100755
--- a/libvideoeditor/lvpp/VideoEditorPlayer.h
+++ b/libvideoeditor/lvpp/VideoEditorPlayer.h
@@ -45,8 +45,9 @@
         virtual ssize_t         frameSize() const;
         virtual uint32_t        latency() const;
         virtual float           msecsPerFrame() const;
-        virtual status_t        getPosition(uint32_t *position);
-        virtual int             getSessionId();
+        virtual status_t        getPosition(uint32_t *position) const;
+        virtual status_t        getFramesWritten(uint32_t*) const;
+        virtual int             getSessionId() const;
 
         virtual status_t        open(
                 uint32_t sampleRate, int channelCount, audio_channel_mask_t channelMask,