add abstraction layer for pcm reading

src/pcm_reader.h

@@ -0,0 +1,48 @@
+#ifndef PCM_READER_H
+#define PCM_READER_H
+
+typedef struct pcm_reader_t pcm_reader_t;
+
+typedef struct pcm_reader_vtbl_t {
+    const pcm_sample_description_t *(*get_format)(pcm_reader_t *);
+    int64_t (*get_length)(pcm_reader_t *);
+    int64_t (*get_position)(pcm_reader_t *);
+    int (*read_frames)(pcm_reader_t *, void *, unsigned);
+    void (*teardown)(pcm_reader_t **);
+} pcm_reader_vtbl_t;
+
+struct pcm_reader_t {
+    pcm_reader_vtbl_t *vtbl;
+};
+
+static inline
+const pcm_sample_description_t *pcm_get_format(pcm_reader_t *r)
+{
+    return r->vtbl->get_format(r);
+}
+
+static inline
+int64_t pcm_get_length(pcm_reader_t *r)
+{
+    return r->vtbl->get_length(r);
+}
+
+static inline
+int64_t pcm_get_position(pcm_reader_t *r)
+{
+    return r->vtbl->get_position(r);
+}
+
+static inline
+int64_t pcm_read_frames(pcm_reader_t *r, void *data, unsigned nframes)
+{
+    return r->vtbl->read_frames(r, data, nframes);
+}
+
+static inline
+void pcm_teardown(pcm_reader_t **r)
+{
+    (*r)->vtbl->teardown(r);
+}
+
+#endif