music_pipe: continuously check the sample format of all chunks

Provide a debug function which asserts on the sample format of all
chunks.  Call this function in each iteration of the player main loop.

src/pipe.c

@@ -300,3 +300,21 @@ void music_pipe_skip(unsigned num)
 	while (music_pipe.begin != (unsigned)i)
 		music_pipe_shift();
 }
+
+#ifndef NDEBUG
+void music_pipe_check_format(const struct audio_format *current,
+			     int next_index, const struct audio_format *next)
+{
+	const struct audio_format *audio_format = current;
+
+	for (unsigned i = music_pipe.begin; i != music_pipe.end;
+	     i = successor(i)) {
+		const struct music_chunk *chunk = music_pipe_get_chunk(i);
+
+		if (next_index > 0 && i == (unsigned)next_index)
+			audio_format = next;
+
+		assert(chunk->length % audio_format_frame_size(audio_format) == 0);
+	}
+}
+#endif

src/pipe.h

@@ -164,4 +164,9 @@ bool music_pipe_tag(const struct tag *tag);
 
 void music_pipe_skip(unsigned num);
 
+#ifndef NDEBUG
+void music_pipe_check_format(const struct audio_format *current,
+			     int next_index, const struct audio_format *next);
+#endif
+
 #endif

src/player_thread.c

@@ -344,6 +344,12 @@ static void do_play(void)
 			}
 		}
 
+#ifndef NDEBUG
+		music_pipe_check_format(&play_audio_format,
+					player.next_song_chunk,
+					&dc.out_audio_format);
+#endif
+
 		if (decoder_is_idle() && !player.queued &&
 		    pc.next_song != NULL &&
 		    pc.command == PLAYER_COMMAND_NONE) {