Add compat support for FFmpeg < 5.1

The new chlayout API has been introduced in FFmpeg 5.1. Use the old
channel_layout API on older versions.

app/src/util/average.c

@@ -1,26 +0,0 @@
-#include "average.h"
-
-#include <assert.h>
-
-void
-sc_average_init(struct sc_average *avg, unsigned range) {
-    avg->range = range;
-    avg->avg = 0;
-    avg->count = 0;
-}
-
-void
-sc_average_push(struct sc_average *avg, float value) {
-    if (avg->count < avg->range) {
-        ++avg->count;
-    }
-
-    assert(avg->count);
-    avg->avg = ((avg->count - 1) * avg->avg + value) / avg->count;
-}
-
-bool
-sc_average_get(struct sc_average *avg, float *value) {
-    *value = avg->avg;
-    return avg->count;
-}

app/src/util/average.h

@@ -1,36 +0,0 @@
-#ifndef SC_AVERAGE
-#define SC_AVERAGE
-
-#include "common.h"
-
-#include <stdbool.h>
-#include <stdint.h>
-
-struct sc_average {
-    // Current average value
-    float avg;
-
-    // Target range, to update the average as follow:
-    //     avg = ((range - 1) * avg + new_value) / range
-    unsigned range;
-
-    // Number of values pushed when less than range (count <= range).
-    // The purpose is to handle the first (range - 1) values properly.
-    unsigned count;
-};
-
-void
-sc_average_init(struct sc_average *avg, unsigned range);
-
-/* Push a new value to update the "rolling" average */
-void
-sc_average_push(struct sc_average *avg, float value);
-
-/* Get the current average value (if available)
- *
- * An average is available if sc_average_push() has been called at least once.
- */
-bool
-sc_average_get(struct sc_average *avg, float *value);
-
-#endif