lavr: fix the decision for writing directly to the output buffer

If there are any samples remaining in the output fifo from previous conversion
calls, we have to output those samples first instead of doing direct output
of the current samples.

libavresample/utils.c

@@ -254,7 +254,7 @@ int attribute_align_arg avresample_convert(AVAudioResampleContext *avr,
     AudioData input_buffer;
     AudioData output_buffer;
     AudioData *current_buffer;
-    int ret;
+    int ret, direct_output;
 
     /* reset internal buffers */
     if (avr->in_buffer) {
@@ -276,6 +276,7 @@ int attribute_align_arg avresample_convert(AVAudioResampleContext *avr,
     av_dlog(avr, "[start conversion]\n");
 
     /* initialize output_buffer with output data */
+    direct_output = output && av_audio_fifo_size(avr->out_fifo) == 0;
     if (output) {
         ret = ff_audio_data_init(&output_buffer, output, out_plane_size,
                                  avr->out_channels, out_samples,
@@ -295,7 +296,7 @@ int attribute_align_arg avresample_convert(AVAudioResampleContext *avr,
         current_buffer = &input_buffer;
 
         if (avr->upmix_needed && !avr->in_convert_needed && !avr->resample_needed &&
-            !avr->out_convert_needed && output && out_samples >= in_samples) {
+            !avr->out_convert_needed && direct_output && out_samples >= in_samples) {
             /* in some rare cases we can copy input to output and upmix
                directly in the output buffer */
             av_dlog(avr, "[copy] %s to output\n", current_buffer->name);
@@ -343,7 +344,7 @@ int attribute_align_arg avresample_convert(AVAudioResampleContext *avr,
         AudioData *resample_out;
         int consumed = 0;
 
-        if (!avr->out_convert_needed && output && out_samples > 0)
+        if (!avr->out_convert_needed && direct_output && out_samples > 0)
             resample_out = &output_buffer;
         else
             resample_out = avr->resample_out_buffer;
@@ -377,7 +378,7 @@ int attribute_align_arg avresample_convert(AVAudioResampleContext *avr,
     }
 
     if (avr->out_convert_needed) {
-        if (output && out_samples >= current_buffer->nb_samples) {
+        if (direct_output && out_samples >= current_buffer->nb_samples) {
             /* convert directly to output */
             av_dlog(avr, "[convert] %s to output\n", current_buffer->name);
             ret = ff_audio_convert(avr->ac_out, &output_buffer, current_buffer,