draft 1

.gitignore

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+bin/
+obj/

.vscode/launch.json

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+{
+    "version": "0.2.0",
+    "configurations": [
+        {
+            // Use IntelliSense to find out which attributes exist for C# debugging
+            // Use hover for the description of the existing attributes
+            // For further information visit https://github.com/OmniSharp/omnisharp-vscode/blob/master/debugger-launchjson.md
+            "name": ".NET Core Launch (console)",
+            "type": "coreclr",
+            "request": "launch",
+            "preLaunchTask": "build",
+            // If you have changed target frameworks, make sure to update the program path.
+            "program": "${workspaceFolder}/bin/Debug/net5.0/videoRetailor.dll",
+            "args": [],
+            "cwd": "${workspaceFolder}/sample recording sess/",
+            // For more information about the 'console' field, see https://aka.ms/VSCode-CS-LaunchJson-Console
+            "console": "internalConsole",
+            "stopAtEntry": false
+        },
+        {
+            "name": ".NET Core Attach",
+            "type": "coreclr",
+            "request": "attach"
+        }
+    ]
+}

.vscode/tasks.json

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+{
+    "version": "2.0.0",
+    "tasks": [
+        {
+            "label": "build",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "build",
+                "${workspaceFolder}/videoRetailor.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "publish",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "publish",
+                "${workspaceFolder}/videoRetailor.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        },
+        {
+            "label": "watch",
+            "command": "dotnet",
+            "type": "process",
+            "args": [
+                "watch",
+                "run",
+                "${workspaceFolder}/videoRetailor.csproj",
+                "/property:GenerateFullPaths=true",
+                "/consoleloggerparameters:NoSummary"
+            ],
+            "problemMatcher": "$msCompile"
+        }
+    ]
+}

Program.cs

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+using System;
+using System.Linq;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using FFMpegCore;
+
+namespace videoRetailor
+{
+    public class analyzedMedia
+    {
+        public List<string> path { get; set; } = new List<string>();
+        public List<IMediaAnalysis> ffprobed { get; set; } = new List<IMediaAnalysis>();
+        public double TotalSeconds { get { return ffprobed.Sum(ima => ima.Duration.TotalSeconds); } }
+        public double durationVariance { get; set; }
+    }
+    class Program
+    {
+        static async Task Main(string[] args)
+        {
+            Console.WriteLine(Directory.GetCurrentDirectory());
+            var mkvFiles = Directory.GetFiles(Directory.GetCurrentDirectory(), "*.mkv");
+
+            var mediaInfos = new List<analyzedMedia>();
+            var totalTime = new TimeSpan();
+            foreach (var file in mkvFiles.OrderBy(f => f))
+            {
+                var thisMeta = new analyzedMedia();
+                thisMeta.path.Add(file);
+                thisMeta.ffprobed.Add(await FFProbe.AnalyseAsync(file));
+                mediaInfos.Add(thisMeta);
+            }
+            if (mediaInfos.Count < 8)
+            {
+                Console.WriteLine($"there's only {mkvFiles.Length}, can't recombine. just going to send them all as-is.");
+            }
+            else
+            {
+                var afterFirst = mediaInfos.Skip(1).ToList();
+                foreach (var thisMeta in afterFirst)
+                {
+                    totalTime += thisMeta.ffprobed[0].Duration;
+                }
+                var averageTime = totalTime.TotalSeconds / afterFirst.Count();
+                Console.WriteLine($"average time: {averageTime}");
+                foreach (var thisMeta in afterFirst)
+                {
+                    thisMeta.durationVariance = thisMeta.TotalSeconds / averageTime;
+                    Console.WriteLine($"{string.Join(", ", thisMeta.path)}: {thisMeta.TotalSeconds} seconds");
+                    Console.WriteLine($"  duration ratio: {thisMeta.durationVariance}");
+                }
+                Console.WriteLine($"...am I crashing? {afterFirst.Min(af => af.durationVariance)}");
+                while (afterFirst.Count() > 6 &&
+                    (afterFirst.Min(af => af.durationVariance) < 0.9))
+                {
+                    Console.WriteLine("gluestick at the ready.");
+                    var idx = 0;
+                    var targetMinDuration = afterFirst.Min(af => af.durationVariance);
+                    Console.WriteLine($"targetMinDuration = {targetMinDuration}");
+                    foreach (var af in afterFirst)
+                    {
+                        if (af.durationVariance == targetMinDuration)
+                        {
+                            break;
+                        }
+                        idx++;
+                    }
+                    var previousDuration = (idx == 0) ? Double.MaxValue : afterFirst[idx - 1].TotalSeconds;
+                    var nextDuration = (idx > afterFirst.Count() - 2) ? Double.MaxValue : afterFirst[idx - 1].TotalSeconds;
+                    analyzedMedia partner;
+                    if (nextDuration > previousDuration)
+                    {
+                        partner = afterFirst[idx - 1];
+                        Console.WriteLine($"combining with previous, previously at {partner.TotalSeconds}");
+                        partner.ffprobed.AddRange(afterFirst[idx].ffprobed);
+                        partner.path.AddRange(afterFirst[idx].path);
+                    }
+                    else
+                    {
+                        partner = afterFirst[idx + 1];
+                        Console.WriteLine($"combining with next, previously at {partner.TotalSeconds}");
+                        afterFirst[idx].ffprobed.AddRange(partner.ffprobed);
+                        partner.ffprobed = afterFirst[idx].ffprobed;
+                        afterFirst[idx].path.AddRange(partner.path);
+                        partner.path = afterFirst[idx].path;
+                    }
+                    afterFirst.RemoveAt(idx);
+                    averageTime = totalTime.TotalSeconds / afterFirst.Count();
+                    foreach (var thisMeta in afterFirst)
+                    {
+                        thisMeta.durationVariance = thisMeta.TotalSeconds / averageTime;
+                    }
+                }
+                mediaInfos = mediaInfos.Take(1).Union(afterFirst).ToList();
+            }
+            Console.WriteLine($"{mediaInfos.Count()} infos.");
+            var i = 1;
+            foreach (var mi in mediaInfos)
+            {
+                Console.WriteLine($"going to export {string.Join(", ", mi.path)} as part {i}");
+                FFMpeg.Join($"./{DateTime.Today.ToShortDateString()} part{i}.mp4",
+                    mi.path.ToArray()
+                );
+
+                i++;
+            }
+        }
+    }
+}

videoRetailor.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="ffmpegcore" Version="4.5.0" />
+  </ItemGroup>
+
+</Project>