diff --git a/libs/audio/include/psemek/audio/combine/mixer.hpp b/libs/audio/include/psemek/audio/combine/mixer.hpp
index 1796978a..d4d0f296 100644
--- a/libs/audio/include/psemek/audio/combine/mixer.hpp
+++ b/libs/audio/include/psemek/audio/combine/mixer.hpp
@@ -15,6 +15,7 @@ namespace psemek::audio
 		virtual channel_ptr add(stream_ptr stream) = 0;
 
 		virtual std::size_t stream_count() const = 0;
+		virtual std::size_t max_length() const = 0;
 	};
 
 	using mixer_ptr = std::shared_ptr<mixer>;
diff --git a/libs/audio/source/combine/mixer.cpp b/libs/audio/source/combine/mixer.cpp
index 98c5e69c..24e00958 100644
--- a/libs/audio/source/combine/mixer.cpp
+++ b/libs/audio/source/combine/mixer.cpp
@@ -22,6 +22,8 @@ namespace psemek::audio
 				return stream_count_.load();
 			}
 
+			std::size_t max_length() const override;
+
 			std::size_t read(util::span<float> samples) override;
 
 			std::optional<std::size_t> length() const override
@@ -59,6 +61,17 @@ namespace psemek::audio
 			return result;
 		}
 
+		std::size_t mixer_impl::max_length() const
+		{
+			// TODO: safe access when the mixer is already playing?
+			std::size_t result = 0;
+			for (auto const & channel : new_channels_)
+				if (auto stream = channel->stream())
+					if (auto length = stream->length(); length && *length > result)
+						result = *length;
+			return result;
+		}
+
 		std::size_t mixer_impl::read(util::span<float> samples)
 		{
 			{