feat(backend): YouTube Music search and playback resolution endpoints

backend/Directory.Packages.props

@@ -19,6 +19,7 @@
     <PackageVersion Include="Microsoft.EntityFrameworkCore" Version="10.0.8" />
     <PackageVersion Include="Microsoft.EntityFrameworkCore.Design" Version="10.0.8" />
     <PackageVersion Include="Microsoft.EntityFrameworkCore.Relational" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Extensions.Configuration" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Extensions.Configuration.Binder" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Extensions.Configuration.FileExtensions" Version="10.0.8" />
@@ -46,6 +47,7 @@
     <PackageVersion Include="X.PagedList" Version="10.5.9" />
     <PackageVersion Include="X.PagedList.EF" Version="10.5.9" />
     <PackageVersion Include="Yarp.ReverseProxy" Version="2.3.0" />
+    <PackageVersion Include="YouTubeMusicAPI" Version="3.0.7" />
   </ItemGroup>
 
 </Project>

backend/Musify.Api/AppSettings.Development.json

@@ -47,6 +47,9 @@
     "OpenTelemetry": {
         "OtlpEndpoint": "http://localhost:4317"
     },
+    "YouTube": {
+        "GeographicalLocation": "ES"
+    },
     "Workers": {
         "Routes": {
             "TemporaryFilesDirectory": "D:\\tempsFilesDev"

backend/Musify.Api/AppSettings.json

@@ -48,6 +48,11 @@
     "OpenTelemetry": {
         "OtlpEndpoint": ""
     },
+    "YouTube": {
+        "GeographicalLocation": "US",
+        "StreamUrlCacheSeconds": 1800,
+        "SearchContinuationCacheSeconds": 600
+    },
     "PlayList": {
         "Routes": {
             "UploadsFolder": "uploads",

backend/Musify.Api/Endpoints/YouTubeEndpoints.cs

@@ -0,0 +1,61 @@
+using Mediator;
+using Musify.Api.Authentication;
+using Musify.Api.Extensions;
+using Musify.Application.Contracts;
+using Musify.Application.YouTube;
+using Musify.Application.YouTube.Responses;
+
+namespace Musify.Api.Endpoints;
+
+public static class YouTubeEndpoints
+{
+    public static IEndpointRouteBuilder MapYouTubeEndpoints(this IEndpointRouteBuilder app)
+    {
+        var group = app.MapGroup("/youtube")
+            .WithTags("YouTube");
+
+        group.MapGet("/search", SearchTracks)
+            .WithName("SearchYouTubeTracks")
+            .WithSummary("Search Songs On YouTube Music.")
+            .RequireAuthorization()
+            .Produces<YouTubeSearchResult>()
+            .Produces(StatusCodes.Status401Unauthorized)
+            .ProducesValidationProblem();
+
+        group.MapGet("/tracks/{videoId}/stream", GetTrackStream)
+            .WithName("GetYouTubeTrackStream")
+            .WithSummary("Resolve Playback For A YouTube Track: Server Stream If Downloaded, Direct YouTube Stream Otherwise.")
+            .RequireAuthorization()
+            .Produces<YouTubeStreamResponse>()
+            .Produces(StatusCodes.Status401Unauthorized)
+            .Produces(StatusCodes.Status404NotFound);
+
+        return app;
+    }
+
+    private static async Task<IResult> GetTrackStream(
+        IMediator mediator,
+        CurrentUser currentUser,
+        string videoId,
+        CancellationToken cancellationToken)
+    {
+        var result = await mediator.Send(
+            new GetYouTubeTrackStreamQuery(videoId, currentUser.RequiredId),
+            cancellationToken);
+
+        return result.ToHttpResult();
+    }
+
+    private static async Task<IResult> SearchTracks(
+        IMediator mediator,
+        CancellationToken cancellationToken,
+        string query,
+        string? continuation = null)
+    {
+        var result = await mediator.Send(
+            new SearchYouTubeTracksQuery(query, continuation ?? string.Empty),
+            cancellationToken);
+
+        return result.ToHttpResult();
+    }
+}

backend/Musify.Api/Extensions/ServiceCollectionExtensions.cs

@@ -18,6 +18,7 @@ public static class ServiceCollectionExtensions
         services.AddDatabase(configuration);
         services.AddStorageService(configuration);
         services.AddStreamTicketService(configuration);
+        services.AddYouTubeMusicService(configuration);
         services.AddMassTransitClient(configuration);
         services.AddAuthenticationConfiguration(configuration);
         services.AddOpenApiConfiguration();

backend/Musify.Api/Program.cs

@@ -1,3 +1,4 @@
+using System.Text.Json.Serialization;
 using Musify.Infrastructure.Observability;
 using Scalar.AspNetCore;
 using Musify.Api.Endpoints;
@@ -5,6 +6,9 @@ using Musify.Api.Extensions;
 
 var builder = WebApplication.CreateBuilder();
 
+builder.Services.ConfigureHttpJsonOptions(options =>
+    options.SerializerOptions.Converters.Add(new JsonStringEnumConverter()));
+
 const string devCorsPolicy = "dev-cors";
 
 builder.Services
@@ -36,6 +40,7 @@ app.UseAuthorization();
 app
     .MapPlayListEndpoints()
     .MapTrackEndpoints()
-    .MapUserEndpoints();
+    .MapUserEndpoints()
+    .MapYouTubeEndpoints();
 
 app.Run();

backend/Musify.Application/ApplicationDependencyInjection.cs

@@ -12,6 +12,7 @@ public static class ApplicationDependencyInjection
     {
         services.AddMediator();
         services.AddScoped<UploadIntentValidator>();
+        services.AddScoped<TrackStreamIssuer>();
 
         services.AddValidatedOptions<ApplicationStorageConfiguration>(configuration, ApplicationStorageConfiguration.SectionName);
         services.AddValidatedOptions<PlayListConfiguration>(configuration, PlayListConfiguration.SectionName);

backend/Musify.Application/Contracts/IYouTubeDownloaderService.cs

@@ -0,0 +1,9 @@
+namespace Musify.Application.Contracts
+{
+    public record YouTubeDownloadResult(int ExitCode, string StandardError);
+
+    public interface IYouTubeDownloaderService
+    {
+        Task<YouTubeDownloadResult> DownloadAudioAsync(string videoId, string destinationFilePath, CancellationToken cancellationToken);
+    }
+}

backend/Musify.Application/Contracts/IYouTubeMusicService.cs

@@ -0,0 +1,25 @@
+using ErrorOr;
+
+namespace Musify.Application.Contracts
+{
+    public record YouTubeSongResult(
+        string VideoId,
+        string Title,
+        string Artist,
+        string Album,
+        int DurationSeconds,
+        string ThumbnailUrl);
+
+    public record YouTubeSearchResult(
+        IReadOnlyList<YouTubeSongResult> Items,
+        string ContinuationToken);
+
+    public record YouTubeStreamInfo(string Url, int ExpiresInSeconds);
+
+    public interface IYouTubeMusicService
+    {
+        Task<ErrorOr<YouTubeSearchResult>> SearchSongsAsync(string query, string continuationToken, CancellationToken cancellationToken);
+
+        Task<ErrorOr<YouTubeStreamInfo>> GetAudioStreamAsync(string videoId, CancellationToken cancellationToken);
+    }
+}

backend/Musify.Application/Services/TrackStreamIssuer.cs

@@ -0,0 +1,41 @@
+using Musify.Application.Configuration;
+using Musify.Application.Contracts;
+using Musify.Application.Tracks.Responses;
+using Musify.Domain.Entities;
+
+namespace Musify.Application.Services;
+
+public sealed class TrackStreamIssuer(
+    IDatabase database,
+    IStreamTicketService ticketService,
+    TrackConfiguration trackConfiguration,
+    StreamGatewayConfiguration streamGatewayConfiguration)
+{
+    public async Task<TrackStreamResponse> IssueAsync(
+        Guid trackId,
+        string audioFolderName,
+        long userId,
+        CancellationToken cancellationToken)
+    {
+        var folderPath = trackConfiguration.Routes.BuildProcessedAudioPath(audioFolderName);
+        var keyPrefix = $"{folderPath}/";
+
+        var ticket = ticketService.IssueTicket(userId, keyPrefix);
+
+        var manifestUrl = string.Join('/',
+            streamGatewayConfiguration.PublicBaseUrl.TrimEnd('/'),
+            "media",
+            folderPath,
+            streamGatewayConfiguration.AudioFileName);
+
+        var newListeningHistory = new ListeningHistory
+        {
+            UserId = userId,
+            TrackId = trackId,
+        };
+        await database.ListeningHistories.AddAsync(newListeningHistory, cancellationToken);
+        await database.SaveChangesAsync(cancellationToken);
+
+        return new TrackStreamResponse(manifestUrl, ticket.Token, ticket.ExpiresInSeconds);
+    }
+}

backend/Musify.Application/Tracks/GetTrackStream.cs

@@ -2,10 +2,9 @@ using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
-using Musify.Application.Configuration;
 using Musify.Application.Contracts;
+using Musify.Application.Services;
 using Musify.Application.Tracks.Responses;
-using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 
 namespace Musify.Application.Tracks
@@ -15,9 +14,7 @@ namespace Musify.Application.Tracks
 
     public class GetTrackStreamQueryHandler(
         IDatabase database,
-        IStreamTicketService ticketService,
+        TrackStreamIssuer streamIssuer,
-        TrackConfiguration trackConfiguration,
-        StreamGatewayConfiguration streamGatewayConfiguration,
         ILogger<GetTrackStreamQueryHandler> logger)
         : IQueryHandler<GetTrackStreamQuery, ErrorOr<TrackStreamResponse>>
     {
@@ -38,30 +35,11 @@ namespace Musify.Application.Tracks
                 return Error.Conflict(description: "Track audio is not available for streaming yet.");
             }
 
-            var folderPath = trackConfiguration.Routes.BuildProcessedAudioPath(track.AudioFolderName);
+            var response = await streamIssuer.IssueAsync(track.Id, track.AudioFolderName, request.UserId, cancellationToken);
-            var keyPrefix = $"{folderPath}/";
-
-            var ticket = ticketService.IssueTicket(request.UserId, keyPrefix);
-
-            var manifestUrl = string.Join('/',
-                streamGatewayConfiguration.PublicBaseUrl.TrimEnd('/'),
-                "media",
-                folderPath,
-                streamGatewayConfiguration.AudioFileName);
 
             logger.LogInformation("Issued stream ticket for track {TrackId} to user {UserId}", request.TrackId, request.UserId);
 
-            var newListeningHistory = new ListeningHistory
+            return response;
-            {
-                UserId = request.UserId,
-                TrackId = request.TrackId,
-            };
-            await database.ListeningHistories.AddAsync(newListeningHistory, cancellationToken);
-            await database.SaveChangesAsync(cancellationToken);
-
-            logger.LogDebug("Listening history added for track {TrackId} by user {UserId}", request.TrackId, request.UserId);
-
-            return new TrackStreamResponse(manifestUrl, ticket.Token, ticket.ExpiresInSeconds);
         }
     }
 }

backend/Musify.Application/YouTube/GetYouTubeTrackStream.cs

@@ -0,0 +1,52 @@
+using ErrorOr;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Musify.Application.Contracts;
+using Musify.Application.Services;
+using Musify.Application.YouTube.Responses;
+using Musify.Domain.ValueObjects;
+
+namespace Musify.Application.YouTube
+{
+    public record GetYouTubeTrackStreamQuery(string VideoId, long UserId)
+        : IQuery<ErrorOr<YouTubeStreamResponse>>;
+
+    public class GetYouTubeTrackStreamQueryHandler(
+        IDatabase database,
+        IYouTubeMusicService youTubeMusicService,
+        TrackStreamIssuer streamIssuer)
+        : IQueryHandler<GetYouTubeTrackStreamQuery, ErrorOr<YouTubeStreamResponse>>
+    {
+        public async ValueTask<ErrorOr<YouTubeStreamResponse>> Handle(GetYouTubeTrackStreamQuery request, CancellationToken cancellationToken)
+        {
+            var track = await database.Tracks.AsNoTracking()
+                .Where(t => t.Source == TrackSource.YouTube && t.ExternalId == request.VideoId)
+                .Select(t => new { t.Id, t.AudioTranscodeProcessingStatus, t.AudioFolderName } )
+                .SingleOrDefaultAsync(cancellationToken);
+
+            if (track != null
+                && !string.IsNullOrWhiteSpace(track.AudioFolderName)
+                && track.AudioTranscodeProcessingStatus == ProcessingStatus.Completed)
+            {
+                var serverStream = await streamIssuer.IssueAsync(track.Id, track.AudioFolderName, request.UserId, cancellationToken);
+                return new YouTubeStreamResponse(
+                    YouTubeStreamMode.Server,
+                    serverStream.ManifestUrl,
+                    serverStream.Ticket,
+                    serverStream.ExpiresInSeconds,
+                    track.Id);
+            }
+
+            var streamInfo = await youTubeMusicService.GetAudioStreamAsync(request.VideoId, cancellationToken);
+            if (streamInfo.IsError)
+                return streamInfo.Errors;
+
+            return new YouTubeStreamResponse(
+                YouTubeStreamMode.YouTube,
+                streamInfo.Value.Url,
+                string.Empty,
+                streamInfo.Value.ExpiresInSeconds,
+                Guid.Empty);
+        }
+    }
+}

backend/Musify.Application/YouTube/Responses/YouTubeStreamResponse.cs

@@ -0,0 +1,15 @@
+namespace Musify.Application.YouTube.Responses
+{
+    public enum YouTubeStreamMode
+    {
+        Server = 0,
+        YouTube = 1
+    }
+
+    public record YouTubeStreamResponse(
+        YouTubeStreamMode Mode,
+        string StreamUrl,
+        string Ticket,
+        int ExpiresInSeconds,
+        Guid TrackId);
+}

backend/Musify.Application/YouTube/SearchYouTubeTracks.cs

@@ -0,0 +1,21 @@
+using ErrorOr;
+using Mediator;
+using Musify.Application.Contracts;
+
+namespace Musify.Application.YouTube
+{
+    public record SearchYouTubeTracksQuery(string Query, string ContinuationToken)
+        : IQuery<ErrorOr<YouTubeSearchResult>>;
+
+    public class SearchYouTubeTracksQueryHandler(IYouTubeMusicService youTubeMusicService)
+        : IQueryHandler<SearchYouTubeTracksQuery, ErrorOr<YouTubeSearchResult>>
+    {
+        public async ValueTask<ErrorOr<YouTubeSearchResult>> Handle(SearchYouTubeTracksQuery request, CancellationToken cancellationToken)
+        {
+            if (string.IsNullOrEmpty(request.Query))
+                return Error.Validation(description: "The search query must not be empty.");
+
+            return await youTubeMusicService.SearchSongsAsync(request.Query, request.ContinuationToken, cancellationToken);
+        }
+    }
+}

backend/Musify.Infrastructure/Configuration/YouTubeConfiguration.cs

@@ -0,0 +1,18 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Musify.Infrastructure.Configuration
+{
+    public class YouTubeConfiguration
+    {
+        public const string SectionName = "YouTube";
+
+        [Required]
+        public string GeographicalLocation { get; set; } = "US";
+
+        [Range(60, 21600)]
+        public int StreamUrlCacheSeconds { get; set; } = 1800;
+
+        [Range(60, 3600)]
+        public int SearchContinuationCacheSeconds { get; set; } = 600;
+    }
+}

backend/Musify.Infrastructure/Configuration/YtDlpConfiguration.cs

@@ -0,0 +1,20 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Musify.Infrastructure.Configuration
+{
+    public class YtDlpConfiguration
+    {
+        public const string SectionName = "YtDlp";
+
+        [Required]
+        public string ExecutableName { get; set; } = "yt-dlp";
+
+        [Required]
+        public string Format { get; set; } = "bestaudio";
+
+        public string AdditionalArguments { get; set; } = string.Empty;
+
+        [Required]
+        public TimeSpan DownloadTimeout { get; set; } = TimeSpan.FromMinutes(5);
+    }
+}

backend/Musify.Infrastructure/Musify.Infrastructure.csproj

@@ -14,6 +14,7 @@
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
+    <PackageReference Include="Microsoft.Extensions.Caching.Memory" />
     <PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" />
     <PackageReference Include="Microsoft.Extensions.Configuration.UserSecrets" />
@@ -28,6 +29,7 @@
     <PackageReference Include="OpenTelemetry.Instrumentation.Process" />
     <PackageReference Include="OpenTelemetry.Instrumentation.Runtime" />
     <PackageReference Include="SixLabors.ImageSharp" />
+    <PackageReference Include="YouTubeMusicAPI" />
   </ItemGroup>
 
   <ItemGroup>

backend/Musify.Infrastructure/Services/ServicesDependencyInjection.cs

@@ -74,6 +74,23 @@ namespace Musify.Infrastructure.Services
             return serviceDescriptors;
         }
 
+        public static IServiceCollection AddYouTubeMusicService(this IServiceCollection serviceDescriptors, IConfiguration configuration)
+        {
+            serviceDescriptors.AddValidatedOptions<YouTubeConfiguration>(configuration, YouTubeConfiguration.SectionName);
+
+            serviceDescriptors.AddMemoryCache();
+            serviceDescriptors.AddSingleton<IYouTubeMusicService, YouTubeMusicService>();
+            return serviceDescriptors;
+        }
+
+        public static IServiceCollection AddYouTubeDownloader(this IServiceCollection serviceDescriptors, IConfiguration configuration)
+        {
+            serviceDescriptors.AddValidatedOptions<YtDlpConfiguration>(configuration, YtDlpConfiguration.SectionName);
+
+            serviceDescriptors.AddScoped<IYouTubeDownloaderService, YouTubeDownloaderService>();
+            return serviceDescriptors;
+        }
+
         public static IServiceCollection AddAudioTranscoder(this IServiceCollection serviceDescriptors, IConfiguration configuration)
         {
             serviceDescriptors

backend/Musify.Infrastructure/Services/YouTubeDownloaderService.cs

@@ -0,0 +1,89 @@
+using Microsoft.Extensions.Logging;
+using Musify.Application.Contracts;
+using Musify.Infrastructure.Configuration;
+using System.Diagnostics;
+
+namespace Musify.Infrastructure.Services
+{
+    public class YouTubeDownloaderService(
+        ILogger<YouTubeDownloaderService> logger,
+        YtDlpConfiguration configuration)
+        : IYouTubeDownloaderService
+    {
+        public async Task<YouTubeDownloadResult> DownloadAudioAsync(string videoId, string destinationFilePath, CancellationToken cancellationToken)
+        {
+            var destinationDirectory = Path.GetDirectoryName(destinationFilePath);
+            if (!string.IsNullOrWhiteSpace(destinationDirectory))
+                Directory.CreateDirectory(destinationDirectory);
+
+            var additionalArguments = string.IsNullOrWhiteSpace(configuration.AdditionalArguments)
+                ? string.Empty
+                : $" {configuration.AdditionalArguments.Trim()}";
+
+            var arguments =
+                $"-f {configuration.Format} " +
+                "--no-playlist " +
+                $"-o \"{destinationFilePath}\"" +
+                additionalArguments +
+                $" -- {videoId}";
+
+            using var process = new Process
+            {
+                StartInfo = new ProcessStartInfo
+                {
+                    FileName = configuration.ExecutableName,
+                    WorkingDirectory = destinationDirectory ?? Environment.CurrentDirectory,
+                    Arguments = arguments,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true,
+                    UseShellExecute = false,
+                    CreateNoWindow = true,
+                }
+            };
+
+            process.Start();
+
+            logger.LogInformation("yt-dlp started (PID: {ProcessId} ) for video {VideoId}", process.Id, videoId);
+
+            var outputTask = process.StandardOutput.ReadToEndAsync(cancellationToken);
+            var errorTask = process.StandardError.ReadToEndAsync(cancellationToken);
+
+            using var linkedCancellationTokens = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+            linkedCancellationTokens.CancelAfter(configuration.DownloadTimeout);
+
+            try
+            {
+                await process.WaitForExitAsync(linkedCancellationTokens.Token);
+            }
+            catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
+            {
+                logger.LogError("yt-dlp timed out after {Timeout} for video {VideoId} (PID: {ProcessId} )",
+                    configuration.DownloadTimeout, videoId, process.Id);
+
+                TryKillProcess(process);
+                throw new TimeoutException($"yt-dlp execution exceeded timeout {configuration.DownloadTimeout}.");
+            }
+
+            var standardError = await errorTask;
+            var standardOutput = await outputTask;
+
+            logger.LogDebug("yt-dlp finished (PID: {ProcessId} ). Exit code: {ExitCode}, Output: {OutputLength}B, Error: {ErrorLength}B",
+                process.Id, process.ExitCode, standardOutput.Length, standardError.Length);
+
+            return new YouTubeDownloadResult(process.ExitCode, standardError);
+        }
+
+        void TryKillProcess(Process process)
+        {
+            try
+            {
+                if (!process.HasExited)
+                    process.Kill();
+            }
+            catch (Exception exception)
+            {
+                logger.LogError(exception, "Failed to kill yt-dlp process (PID: {ProcessId} )", process.Id);
+            }
+        }
+    }
+}

backend/Musify.Infrastructure/Services/YouTubeMusicService.cs

@@ -0,0 +1,114 @@
+using ErrorOr;
+using Microsoft.Extensions.Caching.Memory;
+using Musify.Application.Contracts;
+using Musify.Infrastructure.Configuration;
+using YouTubeMusicAPI.Client;
+using YouTubeMusicAPI.Models.Search;
+using YouTubeMusicAPI.Models.Streaming;
+using YouTubeMusicAPI.Pagination;
+
+namespace Musify.Infrastructure.Services
+{
+    public class YouTubeMusicService(YouTubeConfiguration configuration, IMemoryCache cache) : IYouTubeMusicService
+    {
+        private readonly YouTubeMusicClient client = new(geographicalLocation: configuration.GeographicalLocation);
+
+        private sealed record CachedStreamInfo(string Url, DateTime ExpiresAtUtc);
+
+        public async Task<ErrorOr<YouTubeSearchResult>> SearchSongsAsync(string query, string continuationToken, CancellationToken cancellationToken)
+        {
+            PaginatedAsyncEnumerable<SearchResult>? paginator;
+            if (string.IsNullOrEmpty(continuationToken))
+            {
+                paginator = client.SearchAsync(query, SearchCategory.Songs);
+            }
+            else if (!cache.TryGetValue(SearchCacheKey(continuationToken), out paginator) || paginator is null)
+            {
+                return Error.NotFound(description: "The search continuation has expired.");
+            }
+
+            IReadOnlyList<SearchResult> results;
+            try
+            {
+                results = await paginator.FetchNextPageAsync(cancellationToken);
+            }
+            catch (Exception exception)
+            {
+                return Error.Failure(description: $"YouTube Music search failed: {exception.Message}");
+            }
+
+            var items = results
+                .OfType<SongSearchResult>()
+                .Select(song => new YouTubeSongResult(
+                    song.Id,
+                    song.Name,
+                    string.Join(", ", song.Artists.Select(artist => artist.Name)),
+                    song.Album?.Name ?? string.Empty,
+                    (int)song.Duration.TotalSeconds,
+                    song.Thumbnails
+                        .OrderByDescending(thumbnail => thumbnail.Width)
+                        .Select(thumbnail => thumbnail.Url)
+                        .FirstOrDefault() ?? string.Empty))
+                .ToList();
+
+            var nextToken = string.Empty;
+            if (paginator.HasMore)
+            {
+                nextToken = Guid.NewGuid().ToString("N");
+                cache.Set(
+                    SearchCacheKey(nextToken),
+                    paginator,
+                    TimeSpan.FromSeconds(configuration.SearchContinuationCacheSeconds));
+            }
+
+            return new YouTubeSearchResult(items, nextToken);
+        }
+
+        public async Task<ErrorOr<YouTubeStreamInfo>> GetAudioStreamAsync(string videoId, CancellationToken cancellationToken)
+        {
+            var now = DateTime.UtcNow;
+            if (cache.TryGetValue(StreamCacheKey(videoId), out CachedStreamInfo? cached)
+                && cached is not null
+                && cached.ExpiresAtUtc > now)
+            {
+                return new YouTubeStreamInfo(cached.Url, (int)(cached.ExpiresAtUtc - now).TotalSeconds);
+            }
+
+            StreamingData streamingData;
+            try
+            {
+                streamingData = await client.GetStreamingDataAsync(videoId, cancellationToken);
+            }
+            catch (Exception exception)
+            {
+                return Error.Failure(description: $"Failed to resolve YouTube stream for '{videoId}': {exception.Message}");
+            }
+
+            var audioStream = streamingData.StreamInfo
+                .OfType<AudioStreamInfo>()
+                .OrderByDescending(stream => stream.Bitrate)
+                .FirstOrDefault();
+
+            if (audioStream is null || string.IsNullOrEmpty(audioStream.Url))
+                return Error.NotFound(description: $"No audio stream available for '{videoId}'.");
+
+            var expiresInSeconds = Math.Min(
+                configuration.StreamUrlCacheSeconds,
+                (int)streamingData.ExpiresIn.TotalSeconds);
+
+            if (expiresInSeconds > 0)
+            {
+                cache.Set(
+                    StreamCacheKey(videoId),
+                    new CachedStreamInfo(audioStream.Url, now.AddSeconds(expiresInSeconds)),
+                    TimeSpan.FromSeconds(expiresInSeconds));
+            }
+
+            return new YouTubeStreamInfo(audioStream.Url, expiresInSeconds);
+        }
+
+        private static string SearchCacheKey(string token) => $"yt-search:{token}";
+
+        private static string StreamCacheKey(string videoId) => $"yt-stream:{videoId}";
+    }
+}