audio: fix compilation with older libavresample versions

The libavresample version of the current Libav stable release lacks the
avresample_set_channel_mapping() function. (FFmpeg's libswresample seems
to be fine, because they added swr_set_channel_mapping() first.)

Add a cheap/slow workaround to do channel reordering on our own. We
don't use the recently removed MPlayer code (see commit 586b75a),
because that is not generic enough.

The functionality should be the same as with full-featured
libavresample, and any differences are bugs. It's probably slower,
though.

audio/filter/af_lavrresample.c

@@ -34,6 +34,7 @@
 
 #if defined(CONFIG_LIBAVRESAMPLE)
 #include <libavresample/avresample.h>
+#define USE_SET_CHANNEL_MAPPING HAVE_AVRESAMPLE_SET_CHANNEL_MAPPING
 #elif defined(CONFIG_LIBSWRESAMPLE)
 #include <libswresample/swresample.h>
 #define AVAudioResampleContext SwrContext
@@ -44,6 +45,7 @@
 #define avresample_convert(ctx, out, out_planesize, out_samples, in, in_planesize, in_samples) \
     swr_convert(ctx, out, out_samples, (const uint8_t**)(in), in_samples)
 #define avresample_set_channel_mapping swr_set_channel_mapping
+#define USE_SET_CHANNEL_MAPPING 1
 #else
 #error "config.h broken"
 #endif
@@ -52,6 +54,7 @@
 #include "core/subopt-helper.h"
 #include "audio/filter/af.h"
 #include "audio/fmt-conversion.h"
+#include "audio/reorder_ch.h"
 
 struct af_resample_opts {
     int filter_size;
@@ -217,11 +220,13 @@ static int control(struct af_instance *af, int cmd, void *arg)
             av_opt_set_int(s->avrctx_out, "in_sample_rate", s->ctx.out_rate, 0);
             av_opt_set_int(s->avrctx_out, "out_sample_rate", s->ctx.out_rate, 0);
 
+#if USE_SET_CHANNEL_MAPPING
             // API has weird requirements, quoting avresample.h:
             //  * This function can only be called when the allocated context is not open.
             //  * Also, the input channel layout must have already been set.
             avresample_set_channel_mapping(s->avrctx, s->reorder_in);
             avresample_set_channel_mapping(s->avrctx_out, s->reorder_out);
+#endif
 
             if (avresample_open(s->avrctx) < 0 ||
                 avresample_open(s->avrctx_out) < 0)
@@ -322,12 +327,17 @@ static struct mp_audio *play(struct af_instance *af, struct mp_audio *data)
                                           s->ctx.out_rate, s->ctx.in_rate,
                                           AV_ROUND_UP);
 
+#if USE_SET_CHANNEL_MAPPING
+    reorder_channels(data->audio, s->reorder_in, data->bps, data->nch, in_samples);
+#endif
+
     out_samples = avresample_convert(s->avrctx,
             (uint8_t **) &out->audio, out_size, out_samples,
             (uint8_t **) &in->audio,  in_size,  in_samples);
 
     *data = *out;
 
+#if USE_SET_CHANNEL_MAPPING
     if (needs_reorder(s->reorder_out, out->nch)) {
         if (talloc_get_size(s->reorder_buffer) < out_size)
             s->reorder_buffer = talloc_realloc_size(s, s->reorder_buffer, out_size);
@@ -336,6 +346,9 @@ static struct mp_audio *play(struct af_instance *af, struct mp_audio *data)
                 (uint8_t **) &data->audio, out_size, out_samples,
                 (uint8_t **) &out->audio, out_size, out_samples);
     }
+#else
+    reorder_channels(data->audio, s->reorder_out, out->bps, out->nch, out_samples);
+#endif
 
     data->len = out->bps * out_samples * out->nch;
     return data;

audio/reorder_ch.c

@@ -22,8 +22,10 @@
 
 #include <inttypes.h>
 #include <string.h>
+#include <assert.h>
 
-#include "audio/reorder_ch.h"
+#include "chmap.h"
+#include "reorder_ch.h"
 
 static inline void reorder_to_planar_(void *restrict out, const void *restrict in,
                                       size_t size, size_t nchan, size_t nmemb)
@@ -92,3 +94,52 @@ void reorder_to_packed(uint8_t *out, uint8_t **in,
     else
         reorder_to_packed_(out, in, size, nchan, nmemb);
 }
+
+#define MAX_SAMPLESIZE 8
+
+static void reorder_channels_(uint8_t *restrict data, int *restrict ch_order,
+                              size_t sample_size, size_t num_ch,
+                              size_t num_frames)
+{
+    char buffer[MP_NUM_CHANNELS * MAX_SAMPLESIZE];
+    for (size_t f = 0; f < num_frames; f++) {
+        for (uint8_t c = 0; c < num_ch; c++) {
+            memcpy(buffer + sample_size * c, data + sample_size * ch_order[c],
+                   sample_size);
+        }
+        memcpy(data, buffer, sample_size * num_ch);
+        data += num_ch * sample_size;
+    }
+}
+
+// Reorders for each channel:
+//   out[ch] = in[ch_order[ch]] (but in-place)
+// num_ch is the number of channels
+// sample_size is e.g. 2 for s16le
+// full byte size of in/out = num_ch * sample_size * num_frames
+// Do not use this function in new code; use libavresample instead.
+void reorder_channels(void *restrict data, int *restrict ch_order,
+                      size_t sample_size, size_t num_ch, size_t num_frames)
+{
+    // Check 1:1 mapping
+    bool need_reorder = false;
+    for (int n = 0; n < num_ch; n++)
+        need_reorder |= ch_order[n] != n;
+    if (!need_reorder)
+        return;
+    assert(sample_size <= MAX_SAMPLESIZE);
+    assert(num_ch <= MP_NUM_CHANNELS);
+    // See reorder_to_planar() why this is done this way
+    // s16 and float are the most common sample sizes, and 6 channels is the
+    // most common case where reordering is required.
+    if (sample_size == 2 && num_ch == 6)
+        reorder_channels_(data, ch_order, 2, 6, num_frames);
+    else if (sample_size == 2)
+        reorder_channels_(data, ch_order, 2, num_ch, num_frames);
+    else if (sample_size == 4 && num_ch == 6)
+        reorder_channels_(data, ch_order, 4, 6, num_frames);
+    else if (sample_size == 4)
+        reorder_channels_(data, ch_order, 4, num_ch, num_frames);
+    else
+        reorder_channels_(data, ch_order, sample_size, num_ch, num_frames);
+}

audio/reorder_ch.h

@@ -30,4 +30,7 @@ void reorder_to_planar(void *restrict out, const void *restrict in,
 void reorder_to_packed(uint8_t *out, uint8_t **in,
                        size_t size, size_t nchan, size_t nmemb);
 
+void reorder_channels(void *restrict data, int *restrict ch_order,
+                      size_t sample_size, size_t num_ch, size_t num_frames);
+
 #endif /* MPLAYER_REORDER_CH_H */

configure

@@ -2639,15 +2639,25 @@ echores "yes"
 
 
 _resampler=no
+_avresample=no
+_avresample_has_set_channel_mapping=no
+
 echocheck "libavresample >= 1.0.0"
 if test "$_disable_avresample" = no ; then
   if pkg_config_add "libavresample >= 1.0.0" ; then
     _resampler=yes
+    _avresample=yes
     def_resampler='#define CONFIG_LIBAVRESAMPLE'
   fi
 fi
 echores "$_resampler"
 
+if test "$_avresample" = yes ; then
+  echocheck "libavresample avresample_set_channel_mapping() API"
+  statement_check libavresample/avresample.h 'avresample_set_channel_mapping(NULL, NULL)' && _avresample_has_set_channel_mapping=yes
+  echores "$_avresample_has_set_channel_mapping"
+fi
+
 
 if test "$_resampler" = no ; then
   echocheck "libswresample >= 0.15.100"
@@ -2658,10 +2668,17 @@ if test "$_resampler" = no ; then
   echores "$_resampler"
 fi
 
+
 if test "$_resampler" = no ; then
   die "No resampler found. Install libavresample or libswresample (FFmpeg)."
 fi
 
+if test "$_avresample_has_set_channel_mapping" = yes ; then
+  def_avresample_has_set_channel_mapping='#define HAVE_AVRESAMPLE_SET_CHANNEL_MAPPING 1'
+else
+  def_avresample_has_set_channel_mapping='#define HAVE_AVRESAMPLE_SET_CHANNEL_MAPPING 0'
+fi
+
 
 echocheck "libavutil QP API"
 _avutil_has_qp_api=no
@@ -3307,6 +3324,7 @@ $def_xv
 /* FFmpeg */
 $def_encoding
 $def_resampler
+$def_avresample_has_set_channel_mapping
 
 $def_fast_64bit
 $def_pthreads