Add audio quality check

osu.Game/Rulesets/Edit/BeatmapVerifier.cs

@@ -19,8 +19,10 @@ namespace osu.Game.Rulesets.Edit
             // Resources
             new CheckBackgroundPresence(),
             new CheckBackgroundQuality(),
+
             // Audio
             new CheckAudioPresence(),
+            new CheckAudioQuality()
         };
 
         public IEnumerable<Issue> Run(IBeatmap playableBeatmap, WorkingBeatmap workingBeatmap)

osu.Game/Rulesets/Edit/Checks/CheckAudioQuality.cs

@@ -0,0 +1,75 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Collections.Generic;
+using osu.Game.Beatmaps;
+using osu.Game.Rulesets.Edit.Checks.Components;
+
+namespace osu.Game.Rulesets.Edit.Checks
+{
+    public class CheckAudioQuality : ICheck
+    {
+        // This is a requirement as stated in the Ranking Criteria.
+        // See https://osu.ppy.sh/wiki/en/Ranking_Criteria#rules.4
+        private const int max_bitrate = 192;
+
+        // "A song's audio file /.../ must be of reasonable quality. Try to find the highest quality source file available"
+        // There not existing a version with a bitrate of 128 kbps or higher is extremely rare.
+        private const int min_bitrate = 128;
+
+        public CheckMetadata Metadata { get; } = new CheckMetadata(CheckCategory.Resources, "Too high or low audio bitrate");
+
+        public IEnumerable<IssueTemplate> PossibleTemplates => new IssueTemplate[]
+        {
+            new IssueTemplateTooHighBitrate(this),
+            new IssueTemplateTooLowBitrate(this),
+            new IssueTemplateNoBitrate(this)
+        };
+
+        public IEnumerable<Issue> Run(IBeatmap playableBeatmap, IWorkingBeatmap workingBeatmap)
+        {
+            var audioFile = playableBeatmap.Metadata?.AudioFile;
+            if (audioFile == null)
+                yield break;
+
+            var track = workingBeatmap.Track;
+
+            if (track?.Bitrate == null || track.Bitrate.Value == 0)
+                yield return new IssueTemplateNoBitrate(this).Create();
+            else if (track.Bitrate.Value > max_bitrate)
+                yield return new IssueTemplateTooHighBitrate(this).Create(track.Bitrate.Value);
+            else if (track.Bitrate.Value < min_bitrate)
+                yield return new IssueTemplateTooLowBitrate(this).Create(track.Bitrate.Value);
+        }
+
+        public class IssueTemplateTooHighBitrate : IssueTemplate
+        {
+            public IssueTemplateTooHighBitrate(ICheck check)
+                : base(check, IssueType.Problem, "The audio bitrate ({0} kbps) exceeds {1} kbps.")
+            {
+            }
+
+            public Issue Create(int bitrate) => new Issue(this, bitrate, max_bitrate);
+        }
+
+        public class IssueTemplateTooLowBitrate : IssueTemplate
+        {
+            public IssueTemplateTooLowBitrate(ICheck check)
+                : base(check, IssueType.Problem, "The audio bitrate ({0} kbps) is lower than {1} kbps.")
+            {
+            }
+
+            public Issue Create(int bitrate) => new Issue(this, bitrate, min_bitrate);
+        }
+
+        public class IssueTemplateNoBitrate : IssueTemplate
+        {
+            public IssueTemplateNoBitrate(ICheck check)
+                : base(check, IssueType.Error, "The audio bitrate could not be retrieved.")
+            {
+            }
+
+            public Issue Create() => new Issue(this);
+        }
+    }
+}