filter/ffmpeg: interleave the output AVFrame

If the FFmpeg filter outputs planar data, interleave it, just like the
FFmpeg decoder plugin does.

NEWS

@@ -3,6 +3,7 @@ ver 0.22.3 (not yet released)
   - add option "as_directory", making CUE file expansion optional
 * filter
   - fix garbage after "Audio format not supported by filter" message
+  - ffmpeg: support planar output
 
 ver 0.22.2 (2020/10/28)
 * database

src/filter/plugins/FfmpegFilter.cxx

@@ -18,6 +18,7 @@
  */
 
 #include "FfmpegFilter.hxx"
+#include "lib/ffmpeg/Interleave.hxx"
 #include "lib/ffmpeg/SampleFormat.hxx"
 #include "util/ConstBuffer.hxx"
 
@@ -79,5 +80,5 @@ FfmpegFilter::FilterPCM(ConstBuffer<void> src)
 	/* TODO: call av_buffersink_get_frame() repeatedly?  Not
 	   possible with MPD's current Filter API */
 
-	return {frame.GetData(0), frame->nb_samples * GetOutAudioFormat().GetFrameSize()};
+	return Ffmpeg::InterleaveFrame(*frame, interleave_buffer);
 }

src/filter/plugins/FfmpegFilter.hxx

@@ -21,6 +21,7 @@
 #define MPD_FFMPEG_FILTER__HXX
 
 #include "filter/Filter.hxx"
+#include "lib/ffmpeg/Buffer.hxx"
 #include "lib/ffmpeg/Filter.hxx"
 #include "lib/ffmpeg/Frame.hxx"
 
@@ -32,6 +33,8 @@ class FfmpegFilter final : public Filter {
 	Ffmpeg::FilterContext buffer_src, buffer_sink;
 	Ffmpeg::Frame frame;
 
+	FfmpegBuffer interleave_buffer;
+
 	const int in_format, in_sample_rate, in_channels;
 
 	const size_t in_audio_frame_size;