lavr: remove automatic context close/open for resampling compensation

It adds unnecessary complication for insignificant usability improvement.
The user really should know if they'll need resampling compensation before
opening the context.

Note that only the documentation has changed. The current functionality will
still work until the next major bump.

libavresample/avresample.h

@@ -252,11 +252,10 @@ int avresample_set_matrix(AVAudioResampleContext *avr, const double *matrix,
 /**
  * Set compensation for resampling.
  *
- * This can be called anytime after avresample_open(). If resampling was not
+ * This can be called anytime after avresample_open(). If resampling is not
- * being done previously, the AVAudioResampleContext is closed and reopened
+ * automatically enabled because of a sample rate conversion, the
- * with resampling enabled. In this case, any samples remaining in the output
+ * "force_resampling" option must have been set to 1 when opening the context
- * FIFO and the current channel mixing matrix will be restored after reopening
+ * in order to use resampling compensation.
- * the context.
  *
  * @param avr                    audio resample context
  * @param sample_delta           compensation delta, in samples

libavresample/resample.c

@@ -255,9 +255,10 @@ int avresample_set_compensation(AVAudioResampleContext *avr, int sample_delta,
     if (!compensation_distance && sample_delta)
         return AVERROR(EINVAL);
 
+    if (!avr->resample_needed) {
+#if FF_API_RESAMPLE_CLOSE_OPEN
         /* if resampling was not enabled previously, re-initialize the
            AVAudioResampleContext and force resampling */
-    if (!avr->resample_needed) {
         int fifo_samples;
         int restore_matrix = 0;
         double matrix[AVRESAMPLE_MAX_CHANNELS * AVRESAMPLE_MAX_CHANNELS] = { 0 };
@@ -307,6 +308,10 @@ int avresample_set_compensation(AVAudioResampleContext *avr, int sample_delta,
                 goto reinit_fail;
             ff_audio_data_free(&fifo_buf);
         }
+#else
+        av_log(avr, AV_LOG_ERROR, "Unable to set resampling compensation\n");
+        return AVERROR(EINVAL);
+#endif
     }
     c = avr->resample;
     c->compensation_distance = compensation_distance;

libavresample/version.h

@@ -39,4 +39,8 @@
  * the public API and may change, break or disappear at any time.
  */
 
+#ifndef FF_API_RESAMPLE_CLOSE_OPEN
+#define FF_API_RESAMPLE_CLOSE_OPEN (LIBAVRESAMPLE_VERSION_MAJOR < 2)
+#endif
+
 #endif /* AVRESAMPLE_VERSION_H */