+
+ int const ch = film->audio_channels ();
+
+ if (mixdown_to_stereo) {
+ _audio_mapping = AudioMapping (ch, 2);
+ float const overall_gain = 2 / (4 + sqrt(2));
+ float const minus_3dB = 1 / sqrt(2);
+ _audio_mapping.set (dcp::LEFT, 0, overall_gain);
+ _audio_mapping.set (dcp::RIGHT, 1, overall_gain);
+ _audio_mapping.set (dcp::CENTRE, 0, overall_gain * minus_3dB);
+ _audio_mapping.set (dcp::CENTRE, 1, overall_gain * minus_3dB);
+ _audio_mapping.set (dcp::LS, 0, overall_gain);
+ _audio_mapping.set (dcp::RS, 0, overall_gain);
+ _pending_audio.reset (new AudioBuffers (2, 0));
+ } else {
+ _audio_mapping = AudioMapping (ch, ch);
+ _pending_audio.reset (new AudioBuffers (ch, 0));
+ for (int i = 0; i < ch; ++i) {
+ _audio_mapping.set (i, i, 1);
+ }
+ }