public async Task ExecuteResultAsync(ActionContext context)
{
    var response = context.HttpContext.Response;
    response.ContentType = _contentType;
    response.Headers["Accept-Ranges"] = "bytes";
    response.Headers["Connection"] = "close"; 

    var poolBuf = ArrayPool<byte>.Shared.Rent(512 * 1024);

    try
    {
        await using var fs = new FileStream(
            _path, FileMode.Open, FileAccess.Read, FileShare.Read,
            bufferSize: poolBuf.Length, useAsync: true);

        long total = fs.Length;
        var rangeHeader = context.HttpContext.Request.Headers["Range"].ToString();
        var openEnded = rangeHeader.EndsWith("-", StringComparison.Ordinal);

        var (start, intendedEnd) = ParseRange(context.HttpContext.Request, total);

        var end = openEnded
            ? Math.Min(start + poolBuf.Length - 1, total - 1)
            : intendedEnd;

        var length = end - start + 1;
        response.StatusCode = (start == 0 && end == total - 1) ? 200 : 206;
        response.Headers["Content-Range"] = $"bytes {start}-{end}/{total}";
        response.Headers["Content-Length"] = length.ToString();

        fs.Seek(start, SeekOrigin.Begin);
        var ct = context.HttpContext.RequestAborted;
        long remaining = length;

        while (remaining > 0 && !ct.IsCancellationRequested)
        {
            int toRead = (int)Math.Min(poolBuf.Length, remaining);
            int read = await fs.ReadAsync(poolBuf, 0, toRead, ct);
            if (read == 0) break;

            await response.Body.WriteAsync(poolBuf, 0, read, ct);
            await response.Body.FlushAsync(ct);
            remaining -= read;
        }
    }
    finally
    {
        ArrayPool<byte>.Shared.Return(poolBuf);
    }
}

public async Task ExecuteResultAsync(ActionContext context)
{
    var response = context.HttpContext.Response;
    response.ContentType = _contentType;
    response.Headers["Accept-Ranges"] = "bytes";
    response.Headers["Connection"] = "close"; 

    var poolBuf = ArrayPool<byte>.Shared.Rent(512 * 1024);

    try
    {
        await using var fs = new FileStream(
            _path, FileMode.Open, FileAccess.Read, FileShare.Read,
            bufferSize: poolBuf.Length, useAsync: true);

        long total = fs.Length;
        var rangeHeader = context.HttpContext.Request.Headers["Range"].ToString();
        var openEnded = rangeHeader.EndsWith("-", StringComparison.Ordinal);

        var (start, intendedEnd) = ParseRange(context.HttpContext.Request, total);

        var end = openEnded
            ? Math.Min(start + poolBuf.Length - 1, total - 1)
            : intendedEnd;

        var length = end - start + 1;
        response.StatusCode = (start == 0 && end == total - 1) ? 200 : 206;
        response.Headers["Content-Range"] = $"bytes {start}-{end}/{total}";
        response.Headers["Content-Length"] = length.ToString();

        fs.Seek(start, SeekOrigin.Begin);
        var ct = context.HttpContext.RequestAborted;
        long remaining = length;

        while (remaining > 0 && !ct.IsCancellationRequested)
        {
            int toRead = (int)Math.Min(poolBuf.Length, remaining);
            int read = await fs.ReadAsync(poolBuf, 0, toRead, ct);
            if (read == 0) break;

            await response.Body.WriteAsync(poolBuf, 0, read, ct);
            await response.Body.FlushAsync(ct);
            remaining -= read;
        }
    }
    finally
    {
        ArrayPool<byte>.Shared.Return(poolBuf);
    }
}

var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 64 * 1024, useAsync: true);
Response.Headers["X-Accel-Buffering"] = "no";
return File(stream, mimeType, true);

var stream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.Read, bufferSize: 64 * 1024, useAsync: true);
Response.Headers["X-Accel-Buffering"] = "no";
return File(stream, mimeType, true);