diff --git a/src/audio/audio_task.cpp b/src/audio/audio_task.cpp
index baa0a52d..05a06ad1 100644
--- a/src/audio/audio_task.cpp
+++ b/src/audio/audio_task.cpp
@@ -56,18 +56,20 @@ static const char* kTag = "audio_dec";
 
 static constexpr std::size_t kCodecBufferLength = 240 * 4;
 
-Timer::Timer(uint32_t sample_rate, uint32_t total_samples)
-    : sample_rate_(sample_rate),
+Timer::Timer(const codecs::ICodec::OutputFormat& format)
+    : format_(format),
       current_seconds_(0),
       current_sample_in_second_(0),
-      total_duration_seconds_(total_samples / sample_rate) {}
+      total_duration_seconds_(format.total_samples.value_or(0) /
+                              format.num_channels / format.sample_rate_hz) {}
 
 auto Timer::AddSamples(std::size_t samples) -> void {
   bool incremented = false;
   current_sample_in_second_ += samples;
-  while (current_sample_in_second_ >= sample_rate_) {
+  while (current_sample_in_second_ >=
+         format_.sample_rate_hz * format_.num_channels) {
     current_seconds_++;
-    current_sample_in_second_ -= sample_rate_;
+    current_sample_in_second_ -= format_.sample_rate_hz * format_.num_channels;
     incremented = true;
   }
 
@@ -138,8 +140,7 @@ auto AudioTask::BeginDecoding(std::shared_ptr<codecs::IStream> stream) -> bool {
   }
 
   if (open_res->total_samples) {
-    timer_.reset(
-        new Timer(open_res->sample_rate_hz, open_res->total_samples.value()));
+    timer_.reset(new Timer(open_res.value()));
   } else {
     timer_.reset();
   }
diff --git a/src/audio/include/audio_task.hpp b/src/audio/include/audio_task.hpp
index 5614fbbd..72b89ba2 100644
--- a/src/audio/include/audio_task.hpp
+++ b/src/audio/include/audio_task.hpp
@@ -23,12 +23,12 @@ namespace audio {
 
 class Timer {
  public:
-  Timer(uint32_t sample_rate, uint32_t total_samples);
+  Timer(const codecs::ICodec::OutputFormat& format);
 
   auto AddSamples(std::size_t) -> void;
 
  private:
-  uint32_t sample_rate_;
+  codecs::ICodec::OutputFormat format_;
 
   uint32_t current_seconds_;
   uint32_t current_sample_in_second_;
diff --git a/src/codecs/foxenflac.cpp b/src/codecs/foxenflac.cpp
index b1ba348a..b378e47e 100644
--- a/src/codecs/foxenflac.cpp
+++ b/src/codecs/foxenflac.cpp
@@ -64,7 +64,7 @@ auto FoxenFlacDecoder::OpenStream(std::shared_ptr<IStream> input)
 
   uint64_t num_samples = fx_flac_get_streaminfo(flac_, FLAC_KEY_N_SAMPLES);
   if (num_samples > 0) {
-    format.total_samples = num_samples / fs;
+    format.total_samples = num_samples;
   }
 
   return format;
diff --git a/src/codecs/mad.cpp b/src/codecs/mad.cpp
index dfa568d4..f4cfb3b9 100644
--- a/src/codecs/mad.cpp
+++ b/src/codecs/mad.cpp
@@ -92,7 +92,9 @@ auto MadMp3Decoder::OpenStream(std::shared_ptr<IStream> input)
 
   auto vbr_length = GetVbrLength(header);
   if (vbr_length) {
-    output.total_samples = vbr_length;
+    output.total_samples = vbr_length.value() * channels;
+  } else {
+    // FIXME: calculate length using the filesize, assuming CBR.
   }
   return output;
 }
diff --git a/src/codecs/opus.cpp b/src/codecs/opus.cpp
index f5ff471a..e6e3a1af 100644
--- a/src/codecs/opus.cpp
+++ b/src/codecs/opus.cpp
@@ -125,15 +125,7 @@ auto XiphOpusDecoder::OpenStream(std::shared_ptr<IStream> input)
   auto l = op_pcm_total(opus_, -1);
   std::optional<uint32_t> length;
   if (l > 0) {
-    // Output is always downmixed to two channels, but the pcm count does not
-    // reflect this.
-    int channels = op_channel_count(opus_, -1);
-    if (channels == 1) {
-      l *= 2;
-    } else if (channels > 2) {
-      l /= channels * 2;
-    }
-    length = l;
+    length = l * 2;
   }
 
   return OutputFormat{