Fix errors with WAVs containing markers (#2617).

I'm not 100% sure about this but they seem to end up giving audio
packets with no channels and no frames.  Here we handle such packets
better.

3 files changed, 6 insertions, 2 deletions

diff --git a/src/lib/audio_buffers.cc b/src/lib/audio_buffers.cc
index 4f01146f9..0e31793ea 100644
--- a/src/lib/audio_buffers.cc
+++ b/src/lib/audio_buffers.cc
@@ -81,7 +81,7 @@ void
 AudioBuffers::allocate (int channels, int frames)
 {
 	DCPOMATIC_ASSERT (frames >= 0);
-	DCPOMATIC_ASSERT (channels > 0);
+	DCPOMATIC_ASSERT(frames == 0 || channels > 0);
 
 	ScopeGuard sg = [this]() { update_data_pointers(); };
 
diff --git a/src/lib/audio_buffers.h b/src/lib/audio_buffers.h
index 645348aa0..b43179663 100644
--- a/src/lib/audio_buffers.h
+++ b/src/lib/audio_buffers.h
@@ -60,7 +60,7 @@ public:
 	}
 
 	int frames () const {
-		return _data[0].size();
+		return _data.empty() ? 0 : _data[0].size();
 	}
 
 	void set_frames (int f);
diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index efe151530..c3d32bc75 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -266,6 +266,10 @@ deinterleave_audio(AVFrame* frame)
 	auto audio = make_shared<AudioBuffers>(channels, frames);
 	auto data = audio->data();
 
+	if (frames == 0) {
+		return audio;
+	}
+
 	switch (format) {
 	case AV_SAMPLE_FMT_U8:
 	{