shared_ptr<FFmpegAudioStream> f = dynamic_pointer_cast<FFmpegAudioStream> (i);
DCPOMATIC_ASSERT (f);
f->as_xml (node->add_child("AudioStream"));
shared_ptr<FFmpegAudioStream> f = dynamic_pointer_cast<FFmpegAudioStream> (i);
DCPOMATIC_ASSERT (f);
f->as_xml (node->add_child("AudioStream"));