optimization: don't seek to 0 the first time

mitigates #105 but does not solve it.

After we open a file, we are at the beginning of the file.
So if we get a seek request for 0 and we haven't seeked yet,
we ignore it. This works around glitches caused by ffmpeg's
seeking algorithm.

However, it does not solve the case where the user seeks to
a previous item on the playlist and then a file which has already
been played comes up again.

src/file.hpp

@@ -26,6 +26,7 @@ struct GrooveFilePrivate {
     pthread_mutex_t seek_mutex;
     int64_t seek_pos; // -1 if no seek request
     int seek_flush; // whether the seek request wants us to flush the buffer
+    bool ever_seeked;
 
     int eof;
     double audio_clock; // position of the decode head

src/player.cpp

@@ -301,11 +301,9 @@ static void audio_callback(struct SoundIoOutStream *outstream,
 
                 int ret = groove_sink_buffer_get(sink, &p->audio_buf, 0);
                 if (ret == GROOVE_BUFFER_END) {
+                    emit_event(p->eventq, GROOVE_EVENT_NOWPLAYING);
                     p->play_head = NULL;
                     p->play_pos = -1.0;
-                    // emit the event after setting play head so user can check
-                    // the play head
-                    emit_event(p->eventq, GROOVE_EVENT_NOWPLAYING);
                 } else if (ret == GROOVE_BUFFER_YES) {
                     if (p->play_head != p->audio_buf->item)
                         emit_event(p->eventq, GROOVE_EVENT_NOWPLAYING);

src/playlist.cpp

@@ -560,15 +560,18 @@ static int decode_one_frame(struct GroovePlaylist *playlist, struct GrooveFile *
     // handle seek requests
     pthread_mutex_lock(&f->seek_mutex);
     if (f->seek_pos >= 0) {
-        int64_t seek_pos = f->seek_pos;
-        if (seek_pos == 0 && f->audio_st->start_time != AV_NOPTS_VALUE)
-            seek_pos = f->audio_st->start_time;
-        if (av_seek_frame(f->ic, f->audio_stream_index, seek_pos, 0) < 0) {
-            av_log(NULL, AV_LOG_ERROR, "%s: error while seeking\n", f->ic->filename);
-        } else if (f->seek_flush) {
-            every_sink_flush(playlist);
+        if (f->seek_pos != 0 || f->seek_flush || f->ever_seeked) {
+            int64_t seek_pos = f->seek_pos;
+            if (seek_pos == 0 && f->audio_st->start_time != AV_NOPTS_VALUE)
+                seek_pos = f->audio_st->start_time;
+            if (av_seek_frame(f->ic, f->audio_stream_index, seek_pos, 0) < 0) {
+                av_log(NULL, AV_LOG_ERROR, "%s: error while seeking\n", f->ic->filename);
+            } else if (f->seek_flush) {
+                every_sink_flush(playlist);
+            }
+            avcodec_flush_buffers(f->audio_st->codec);
         }
-        avcodec_flush_buffers(f->audio_st->codec);
+        f->ever_seeked = true;
         f->seek_pos = -1;
         f->eof = 0;
     }